Patent Publication Number: US-2019175258-A1

Title: Treatment tool

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of PCT Application No. PCT/JP2016/078709 filed on Sep. 28, 2016, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The disclosed technology relates to a treatment tool. 
     DESCRIPTION OF THE RELATED ART 
     Heretofore, there has been known a treatment tool that treats, e.g., joins or anastomoses and separates, a living tissue by grasping the living tissue with a pair of jaws and applying an energy to the living tissue, i.e., passing a high-frequency electric current through the living tissue (see, for example, Patent Literature (PTL 1)—JP 2010-527704T). 
     PTL 1 discloses various structures for passing a high-frequency electric current widthwise or transversely across the jaws. 
     According to the first structure, for example, one (hereinafter referred to as “first grasping jaw”) of the paired jaws has a first grasping surface for grasping a living tissue between itself and the other jaw (hereinafter referred to as “second grasping jaw”). The first grasping surface has a first electrode disposed on one transverse end side thereof. The second grasping jaw has a second grasping surface for grasping a living tissue between itself and the first grasping surface. The second grasping surface has a second electrode disposed on the other transverse end side thereof. In other words, the first and second electrodes are disposed in transversely staggered positions so that they do not face each other when the first and second grasping jaws are closed. When high-frequency electric power is supplied between the first and second electrodes, a high-frequency electric current flows through the living tissue grasped by the first and second grasping jaws, widthwise across the jaws. 
     According to the second structure, for example, the first grasping surface has a first electrode disposed on one transverse end side thereof. The first grasping surface also has a second electrode disposed on the other transverse end side thereof. When high-frequency electric power is supplied between the first and second electrodes, a high-frequency electric current flows through the living tissue grasped by the first and second grasping jaws, widthwise across the jaws. 
     With the structures described hereinbefore in which the high-frequency electric current flows transversely across the jaws, a region through which the high-frequency electric current flows between the first and second electrodes becomes a heat-generating region. Therefore, a treatment target tissue of the living tissue can be limited to a nearly transversely central region of the jaws between the first and second electrodes. The effect of heat on peripheral tissues that are positioned transversely outside of the jaws in the periphery of the treatment target tissue is thus reduced, allowing the living tissue to be treated minimally invasively. 
     A comparison will hereinafter be made between the structure disclosed in PTL 1 in which a high-frequency electric current flows widthwise across the jaws (hereinafter referred to as “width structure”) and a structure in which a high-frequency electric current flows in a direction along which the jaws face each other (hereinafter referred to as “facing structure”), unlike PTL 1. The facing structure is a structure in which the first grasping surface has a first electrode and the second grasping surface has a second electrode, so that the first and second electrodes face each other when the first and second grasping jaws are closed. 
     The width structure has a long electric current path along which a high-frequency electric current flows through a living tissue, compared with the facing structure. For example, when the first and second grasping jaws grasp a living tissue, the distance between the first and second grasping surfaces is 1 mm or less. Depending on the living tissue, the distance is less than 0.5 mm. In other words, the facing structure has an electric current path that is 1 mm or less long. On the other hand, it is difficult for the width structure to reduce the distance between the first and second electrodes because the treatment target tissue needs to be of a certain size. Consequently, the width structure has an electric current path that is 2 mm or 3 mm or more long. 
     Either the width structure or the facing structure consumes the same amount of high-frequency electric power required for treating a treatment target tissue of one kind and size. On the other hand, the electric resistance value of a living tissue, which means the real part of an electric impedance when a high-frequency electric current flows, increases in proportion to the length of the electric current path and is in inverse proportion to the cross section of the electric current path. In other words, since the length of the electric current path is larger in the width structure than in the facing structure and the cross section of the electric current path is smaller in the width structure than in the facing structure, the electric resistance value of the width structure is higher than the electric resistance value of the facing structure in treating a treatment target tissue of one kind and size. 
     Specifically, it is assumed that the size of a treatment target tissue is represented by a width of 3 mm, a length of 5 mm, and a thickness of 1 mm. In this case, the length of the electric current path of the facing structure is 1 mm, and the cross section thereof is 15 mm 2 . The length of the electric current path of the width structure is 3 mm, and the cross section thereof is 5 mm 2 . As described hereinbefore, the electric resistance value of the living tissue is in proportion to the length of the electric current path and is in inverse proportion to the cross section of the electric current path. Consequently, the electric resistance value of the width structure is nine times the electric resistance value of the facing structure. If the electric resistance value R is nine times larger, then in order to generate the same electric power P, a voltage V that is three times higher is required as can be seen from the following equation (1): 
     
       
         
           
             
               
                 
                   
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     As described hereinbefore, the width structure requires a high voltage compared with the facing structure in treating a treatment target tissue of one kind and size. 
     In order to reduce the voltage, it is necessary to reduce the electric resistance. However, if the distance between the first and second electrodes is simply made shorter, then the size of the treatment target tissue is reduced, possibly resulting in a failure to obtain a desired level of performance after the treatment. 
     Therefore, there is a need for a technology that is capable of reducing a voltage required to treat a treatment target tissue while performing the treatment minimally invasively without reducing the size of the treatment target tissue. 
     BRIEF SUMMARY OF EMBODIMENTS 
     The disclosed technology has been made in view of the foregoing. It is an object of the disclosed technology to provide a treatment tool that is capable of reducing a voltage required to treat a treatment target tissue while performing the treatment minimally invasively without reducing the size of the treatment target tissue. 
     The disclosed technology is directed to a treatment system used for treatment of a body tissue by applying electrical energy thereto. The treatment system comprises a controller and a treatment tool configured to be attached to controller. The treatment tool comprises a shaft having a first end and a second end. A handle is attached to the first end. Respective first and second grasping jaws each of which having respective first and second grasping surfaces configured to be engaged with the second end of the shaft so as to pivot with respect to one another for holding living tissue therebetween during the treatment. A first electrode is disposed on the first grasping surface. A second electrode is disposed on either the first grasping surface or the second grasping surface and is configured to generate high-frequency energy in tandem with the first electrode to the living tissue being held therebetween. At least one floating electrode is disposed in at least one of the respective first and second grasping surfaces so that the treatment tool being capable of reducing a voltage required to treat the body tissue while performing the treatment without reducing a size of the body tissue. 
     The treatment tool according to the disclosed technology is advantageous in that it can perform a treatment minimally invasively and reduce a voltage required for the treatment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The technology disclosed herein, in accordance with one or more various embodiments, is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and merely depict typical or example embodiments of the disclosed technology. These drawings are provided to facilitate the reader&#39;s understanding of the disclosed technology and shall not be considered limiting of the breadth, scope, or applicability thereof. It should be noted that for clarity and ease of illustration these drawings are not necessarily made to scale. 
         FIG. 1  is a view illustrating a treatment tool according to Embodiment 1. 
         FIG. 2  is a view illustrating a grasper illustrated in  FIG. 1 . 
         FIG. 3  is a view illustrating the grasper illustrated in  FIG. 1 . 
         FIG. 4  is a view illustrating the positional relationship of first and second electrodes and a floating electrode illustrated in  FIGS. 2 and 3 . 
         FIG. 5  is a conceptual diagram illustrating the advantages of Embodiment 1. 
         FIG. 6  is a conceptual diagram illustrating the advantages of Embodiment 1. 
         FIG. 7  is a conceptual diagram illustrating the advantages of Embodiment 1. 
         FIG. 8  is a conceptual diagram illustrating the advantages of Embodiment 1. 
         FIG. 9A  is a view illustrating a grasper of a treatment tool according to Embodiment 2, the view depicting a path for a high-frequency electric current in a former part of a treatment process. 
         FIG. 9B  is a view illustrating a grasper of the treatment tool according to Embodiment 2, the view depicting a path for a high-frequency electric current in a latter part of the treatment process. 
         FIG. 10  is a view illustrating a grasper of a treatment tool according to Embodiment 3. 
         FIG. 11  is a view illustrating a floating electrode illustrated in  FIG. 10 . 
         FIG. 12A  is a view depicting a path for a high-frequency electric current in a latter part of a treatment process according to Embodiment 3. 
         FIG. 12B  is a view depicting a path for a high-frequency electric current in a latter part of the treatment process according to Embodiment 3. 
         FIG. 13  is a view illustrating a grasper of a treatment tool according to Embodiment 4. 
         FIG. 14  is a view illustrating a grasper of a treatment tool according to Embodiment 5. 
         FIG. 15  is a view illustrating a grasper of a treatment tool according to Embodiment 6. 
         FIG. 16  is a view illustrating a grasper of a treatment tool according to Embodiment 7. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the following description, various embodiments of the technology will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the embodiments. However, it will also be apparent to one skilled in the art that the technology disclosed herein may be practiced without the specific details. Furthermore, well-known features may be omitted or simplified in order not to obscure the embodiment being described. 
     Forms by which the disclosed technology is embodied, hereinafter referred to as “embodiments,” will hereinafter be described with reference to the drawings. The embodiments to be described hereinafter should not be interpreted as limiting the disclosed technology. Identical parts are denoted by identical numeral reference in figures. 
     Embodiment 1 
     Makeup Outline of a Treatment System 
       FIG. 1  is a view illustrating a treatment system  1  according to present Embodiment 1. 
     The treatment system  1  treats, e.g., joins or anastomoses, separates, or otherwise processes, a living tissue by applying energy, e.g., electric energy (high-frequency energy), to the living tissue. As illustrated in  FIG. 1 , the treatment system  1  includes a treatment tool  2 , a controller  3 , and a foot switch  4 . 
     Makeup of the Treatment Tool 
     The treatment tool  2  is a linear-type surgical treatment tool for treating a living tissue through an abdominal wall, for example. As illustrated in  FIG. 1 , the treatment tool  2  includes a handle  5 , a shaft  6 , and a grasper  7 . 
     The handle  5  is a part by which the surgeon holds the treatment tool  2  by hand. As illustrated in  FIG. 1 , the handle  5  has a manipulating knob  51 . 
     As illustrated in  FIG. 1 , the shaft  6  is of a substantially hollow cylindrical shape and has one end, i.e., a right end in  FIG. 1 , connected to the handle  5 . The grasper  7  is mounted on the other end, i.e., a left end in  FIG. 1 , of the shaft  6 . The shaft  6  houses therein an opening and closing mechanism, not depicted, that opens and closes a first grasping jaw  8  and a second grasping jaw  9  ( FIG. 1 ) that make up the grasper  7  in response to the surgeon&#39;s manipulation of the manipulating knob  51 . An electric cable C ( FIG. 1 ) connected to the controller  3  is housed in the shaft  6  and extends from one end, i.e., a right end in  FIG. 1 , to the other end, i.e., a left end in  FIG. 1 , through the handle  5 . 
     Structure of the Grasper 
     “Longitudinal directions” described hereinafter refer to directions interconnecting the distal and proximal ends of the grasper  7  that is set to a closed state in which it grasps a living tissue LT, i.e., a state in which the first and second grasping jaws  8  and  9  are closed or first and second grasping surfaces  81  and  91  face each other. “Width directions” described hereinafter refer to transverse directions that extend along the first and second grasping surfaces  81  and  91  perpendicularly to the longitudinal directions. 
       FIGS. 2 and 3  are views illustrating the grasper  7 . Specifically,  FIG. 2  is a perspective view illustrating the grasper  7  that is set to an open state in which the first and second grasping jaws  8  and  9  are open or spaced apart.  FIG. 3  is a cross-sectional view taken along a sectional plane along the widthwise directions across the grasper  7  that is set to the closed state in which it grasps the living tissue LT such as a lumen, a blood vessel, or the like. 
     The grasper  7  is a portion for grasping and treating the living tissue LT ( FIG. 3 ). As illustrated in  FIGS. 1 through 3 , the grasper  7  includes the first and second grasping jaws  8  and  9 . 
     The first and second grasping jaws  8  and  9  are pivotally supported on the other end of the shaft  6  for opening and closing movement in the directions indicated by an arrow R 1  ( FIG. 2 ). The first and second grasping jaws  8  and  9  are capable of grasping the living tissue LT in response to a manipulation by the surgeon of the manipulating knob  51 . 
     Makeup of the First Grasping Jaw 
     The first grasping jaw  8  is disposed above the second grasping jaw  9  in  FIGS. 2 and 3 , and is substantially shaped as a rectangular parallelepiped extending along the longitudinal directions. The first grasping jaw  8  may be made of a material that is highly heat-resistant, low in thermal conductivity, and excellent in electric insulation, e.g., a resin such as PTFE (polytetrafluoroethylene), PEEK (polyetheretherketone), PBI (polybenzimidazole), or the like. However, the material of the first grasping jaw  8  is not limited to the concerned resin, but may be ceramics such as alumina, zirconia, or the like. Furthermore, the first grasping jaw  8  may be coated with PTFE, DLC (Diamond-Like Carbon), a ceramics-based insulative coating material, a silica-based insulative coating material, or a silicone-based insulative coating material that is nonadherent to living bodies. 
     The first grasping jaw  8  has a lower surface in  FIGS. 2 and 3  that functions as a grasping surface  81  for grasping the living tissue LT between itself and the second grasping jaw  9 . 
     According to Embodiment 1, the first grasping surface  81  has a flat shape. 
     As illustrated in  FIGS. 2 and 3 , first and second electrodes  10  and  11  are embedded in the first grasping surface  81  at respective areas positioned on both end portions in the widthwise directions or the lateral direction, i.e., on left and right end portions in  FIGS. 2 and 3 , and extending along the entire length, i.e., the entire length in the longitudinal directions, of the first grasping surface  81 . 
     The first and second electrodes  10  and  11  are made of an electrically conductive material such as copper, aluminum, carbon, or the like, for example. Each of the first and second electrodes  10  and  11  is in the form of a plate substantially shaped as a rectangular parallelepiped extending along the longitudinal directions. The first and second electrodes  10  and  11  are embedded in the first grasping surface  81  such that one of the plate surfaces, i.e., the lower surface in  FIGS. 2 and 3 , of each of the first and second electrodes  10  and  11  makes up part of the first grasping surface  81 , i.e., is exposed. The electric cable C, which extends from one end to the other end of the shaft  6 , contains a pair of leads, not depicted, connected respectively to the first and second electrodes  10  and  11 . When the first and second electrodes  10  and  11  are supplied with high-frequency electric power from the controller  3  through the pair of leads, the first and second electrodes  10  and  11  generate high-frequency energy. When the first and second electrodes  10  and  11  are supplied with high-frequency electric power while the first grasping jaw  8  and the second grasping jaw  9 , i.e., the first grasping surface  81  and the second grasping surface  91  thereof, are grasping the living tissue LT, a high-frequency potential is developed between the first and second electrodes  10  and  11 , causing a high-frequency current to flow through the living tissue LT. In other words, the first and second electrodes  10  and  11  are a pair of electrodes where one of them functions as a positive electrode while the other as a negative electrode. 
     The first and second electrodes  10  and  11  are not limited to plates, but may be of a different shape such as round bars embedded in the first grasping jaw  8  and having projected portions that are small as compared with the distance between the first grasping jaw  8  and the second grasping jaw  9 . The first and second electrodes  10  and  11  may not necessarily be made of a bulk material, but may be in the form of electrically conductive thin films of platinum or the like deposited by way of evaporation, sputtering, or the like. Moreover, the surfaces of the first and second electrodes  10  and  11  may not necessarily be physically exposed as described hereinbefore, but may be electrically exposed. Specifically, the surfaces of the first and second electrodes  10  and  11  may be coated with an electrically conductive coating material such as Ni-PTFE film, electrically conductive DLC thin film, or the like that is nonadherent to living bodies, so that the surfaces can function as electrodes to develop a potential. Such alternatives do not depart from the scope of the disclosed technology. 
     Makeup of the Second Grasping Jaw 
     The second grasping jaw  9  is substantially shaped as a rectangular parallelepiped extending along the longitudinal directions. As with the first grasping jaw  8 , the second grasping jaw  9  may be made of a resin such as PTFE, PEEK, PBI, or the like, or ceramics such as alumina, zirconia, or the like, for example. 
     The second grasping jaw  9  has an upper surface in  FIGS. 2 and 3  that functions as the second grasping surface  91  for grasping the living tissue LT between itself and the first grasping surface  81 . 
     According to Embodiment 1, the second grasping surface  91  is shaped flatwise as with the first grasping surface  81 . 
     As illustrated in  FIG. 2 or 3 , the second grasping surface  91  has a floating electrode  12  embedded in an area thereof that is positioned centrally in the width directions, i.e., centrally in the leftward and rightward directions in  FIGS. 2 and 3 , and extends the entire length of the second grasping surface  91 . 
     The floating electrode  12  is made of a good conductor such as copper, aluminum, gold, carbon, or the like, for example. The floating electrode  12  is constructed as a plate in the form of a substantially rectangular parallelepiped extending along the longitudinal directions. The floating electrode  12  is embedded such that one plate surface thereof, i.e., an upper surface in  FIGS. 2 and 3 , serves as part of the second grasping surface  91 , i.e., the one plate surface is exposed. Unlike the first and second electrodes  10  and  11 , the floating electrode  12  is not connected to the controller  3  through a lead, and is not connected to ground, i.e., is electrically floating. 
     The floating electrode  12  is not limited to the shape of the plate, but may be of a different shape such as a round rod or the like embedded such that it may have a protrusive portion that is small compared with the distance between the first and second grasping jaws  8  and  9 . The floating electrode  12  may not necessarily be made of a bulk material, but may be made of a foil or thin film of a good conductor or an electrically conductive DLC thin film or the like that is formed by chemical vapor deposition (CVD) or the like. The surface of the floating electrode  12  may not be physically exposed as described hereinbefore, but may be electrically exposed. In other words, the surface of the floating electrode  12  may be coated with an electrically conductive coating material such as Ni-PTFE film, electrically conductive DLC thin film, or the like which is non-adhesive to living bodies, and may provide a potential as an electrode. Such an alternative does not depart from the scope of the invention. 
     It is known in the art that the living tissue LT has different electric conductivities for different target regions because of different compositions thereof. For example, the volume resistivity at 10 kHz is 30 Ω·m for fat tissue, 7 Ω·m for muscle and liver tissue, and 2 Ω·m for blood. The electric conductivity differs greatly with water contents. It is also well known that the electric conductivity is quickly lost as the tissue becomes dry in the course of the treatment. 
     According to Embodiment 1, the floating electrode  12  has an electric resistance value of 1Ω or less, e.g., 10 mΩ, which is lower than the electric resistance value of 250Ω of the living tissue LT at the electric current path contacted by the floating electrode  12 . 
     Positional Relationship of the First and Second Electrodes and the Floating Electrode 
       FIG. 4  is a view illustrating the positional relationship of the first and second electrodes  10  and  11  and the floating electrode  12 . Specifically,  FIG. 4  is a view of the first and second electrodes  10  and  11  and the floating electrode  12  as viewed along the directions in which the first and second grasping surfaces  81  and  91  face each other when the grasper  7  is in the contact state, i.e., along the directions normal to the first and second grasping surfaces  81  and  91 . 
     As illustrated in  FIG. 4 , when the floating electrode  12  is viewed along the directions in which the first and second grasping surfaces  81  and  91  face each other when the grasper  7  is in the closed state, the floating electrode  12  is disposed between the first and second electrodes  10  and  11 . More specifically, the floating electrode  12  has a transversely central position O 1  that is aligned with a transversely central position O 2  between the first and second electrodes  10  and  11 . 
     As illustrated in  FIG. 3 , the floating electrode  12  has a transverse length W 1  that is larger than a spaced distance D 0  between the first and second grasping surfaces  81  and  91  that are grasping the living tissue LT therebetween. 
     Makeup of the Controller and the Foot Switch 
     The foot switch  4  is a part that the surgeon operates with their foot. When the foot switch  4  is thus operated, the controller  3  selectively turns on and off the treatment tool  2 , i.e., the first and second electrodes  10  and  11 . 
     Means for selectively turning on and off the treatment tool  2  is not limited to the foot switch  4 , but may be a switch that can be operated by hand, etc. 
     The controller  3 , which includes a CPU (Central Processing Unit) and so on, integrally controls operation of the treatment tool  2  according to predetermined control programs. Specifically, in response to the operation of the foot switch  4  by the surgeon to turn on the controller  3 , the controller  3  supplies high-frequency electric power at a preset output level between the first and second electrodes  10  and  11  through the pair of leads. Then, the controller  3  appropriately controls energy levels. 
     Operation of the Treatment System 
     Next, operation of the treatment system  1  described hereinbefore will be described hereinafter. 
     The surgeon holds the treatment tool  2  by hand, and inserts a distal-end portion of the treatment tool  2 , i.e., the grasper  7  and a portion of the shaft  6 , into an abdominal cavity through the abdominal wall using a trocar or the like, for example. The surgeon also operates the manipulating knob  51  to grasp the living tissue LT with the first grasping jaw  8  and the second grasping jaw  9 . 
     Then, the surgeon operates the foot switch  4  to turn on the controller  3  to electrically energize the treatment tool  2 . When the controller  3  is turned on, the controller  3  supplies high-frequency electric power between the first and second electrodes  10  and  11  through the pair of leads. 
     When high-frequency electric power is supplied between the first and second electrodes  10  and  11 , a high-frequency potential is generated between the first and second electrodes  10  and  11 , and the floating electrode  12  is held at a potential that is substantially intermediate between the respective potentials of the first and second electrodes  10  and  11 . As a result, high-frequency electric currents flow between the first and second electrodes  10  and  11  along a path that extends through only the living tissue LT and a path that extends through both the living tissue LT and the floating electrode  12 . The proportions of the respective paths are determined by the difference between the electric resistance values of the living tissue LT and the floating electrode  12 . 
     In the living tissue LT that is grasped by the first and second grasping surfaces  81  and  91 , as viewed along the directions in which the first and second grasping surfaces  81  and  91  face each other, tissues positioned between the first electrode  10  and the floating electrode  12  and between the second electrode  11  and the floating electrode  12  will hereinafter be referred to as tissues LT 1  ( FIG. 3 ), and a tissue positioned between the tissues LT 1  as a tissue LT 2  ( FIG. 3 ). This definition of the tissues also applies to Embodiments 2 through 6 to be described hereinafter. 
     According to Embodiment 1, since the floating electrode  12  is made of a good conductor, as described hereinbefore, the electric resistance value of the floating electrode  12  is far lower than the electric resistance value of the living tissue LT, or more specifically, the tissue LT 2 . Therefore, a high-frequency electric current flows along a path Pa that extends through the tissues LT 1  and the floating electrode  12 , as illustrated in  FIG. 3 . Thus, mainly Joule heat is generated in each of the tissues LT 1 . Each of the tissues LT 1  is treated by the generated Joule heat. Accordingly, each of the tissues LT 1  and LT 2  is a treatment target tissue LT 0  to be treated. 
     Embodiment 1 described hereinbefore offers the following advantages: 
       FIGS. 5 through 8  are conceptual diagrams illustrating the advantages of Embodiment 1. Specifically,  FIGS. 5 and 6  illustrate, respectively, time-dependent changes in the resistance between the first and second electrodes  10  and  11  and time-dependent changes in a voltage Vp between the first and second electrodes  10  and  11  when a constant high-frequency electric power, e.g., of 20 W, is continuously supplied between the first and second electrodes  10  and  11  while the first and second grasping surfaces  81  and  91  are grasping the living tissue LT therebetween. In  FIGS. 5 and 6 , the time-dependent changes with the conventional structure that is free of the floating electrode  12  unlike Embodiment 1 are indicated by the broken-line curves, whereas the time-dependent changes with the structure having the floating electrode  12  according to Embodiment 1 are indicated by the solid-line curves. The solid-line curves in  FIGS. 5 and 6  represent the time-depending changes with the structure having the floating electrode  12  whose electric resistance value is 1/100 of the electric resistance value of the living tissue LT, i.e., the tissue LT 2 , and whose length W 1  is ⅓ of the distance between the first and second electrodes  10  and  11 .  FIGS. 7 and 8  illustrate the relationship between the electric resistance value of the floating electrode  12  and the resistance between the first and second electrodes  10  and  11 , i.e., the combined resistance of the living tissue LT and the floating electrode  12 , and the relationship between the electric resistance value of the floating electrode  12  and the voltage Vp between the first and second electrodes  10  and  11 . 
     The treatment tool  2  according to Embodiment 1 includes, on the second grasping surface  91 , the floating electrode  12  having the electric resistance value lower than the electric resistance value of the living tissue LT, i.e., the tissue LT 2 , between the first and second electrodes  10  and  11  as viewed along the directions in which the first and second grasping surfaces  81  and  91  face each other when the grasper  7  is in the closed state. Therefore, when high-frequency electric power is supplied between the first and second electrodes  10  and  11  while the first and second grasping surfaces  81  and  91  are grasping the living tissue LT therebetween, the floating electrode  12  becomes part of the path Pa of the high-frequency electric current. In other words, the floating electrode  12  is able to reduce the resistance between the first and second electrodes  10  and  11 , i.e., the combined resistance of the living tissue LT and the floating electrode  12 , compared with the conventional structure that is free of the floating electrode  12 . The voltage required to supply predetermined high-frequency electric power between the first and second electrodes  10  and  11  can thus be made lower than with the conventional structure. Furthermore, since the voltage can be reduced simply by disposing the floating electrode  12  without reducing the distance between the first and second electrodes  10  and  11 , the size of the treatment target tissue LT 0  is not reduced. 
     Specifically, as illustrated in  FIG. 5 , in a latter part of the treatment process, i.e., subsequent to eight seconds in  FIG. 5 , the conventional structure indicated by the broken-line curve illustrated in  FIG. 5  exhibits 1000Ω as the resistance between the first and second electrodes  10  and  11 . On the other hand, the structure according to Embodiment 1 indicated by the solid-line curve illustrated in  FIG. 5  exhibits approximately 670Ω as the combined resistance between the first and second electrodes  10  and  11 , which is approximately ⅔ of the conventional structure. Accordingly, as illustrated in  FIG. 6 , the voltage Vp required to supply the high-frequency electric power of 20 W between the first and second electrodes  10  and  11  is 200 Vp with the conventional structure and 164 Vp with the structure according to Embodiment 1, resulting in a drop of 36 Vp. 
     The reduction in the combined resistance and the reduction in the voltage due to the floating electrode  12  are determined by the difference between the electric resistance values of the living tissue LT, more specifically the tissue LT 2 , and the floating electrode  12 . Specifically, as illustrated in  FIG. 7 , the higher the electric resistance value of the tissue LT 2  is, the larger the reduction in the combined resistance due to the floating electrode  12  becomes. As a result, as illustrated in  FIG. 8 , the higher the electric resistance value of the tissue LT 2  is, the larger the reduction in the voltage required to supply the same high-frequency electric power between the first and second electrodes  10  and  11  becomes. Furthermore, it can be seen from  FIGS. 7 and 8  that the electric resistance value of the floating electrode  12  does not need to be extremely low. For example, if the electric resistance value of the tissue LT 2  is 1000Ω, then the reduction in the combined resistance and the reduction in the voltage that are caused when the electric resistance value of the floating electrode  12  is much lower than 100Ω remains essentially the same as those caused when the electric resistance value of the floating electrode  12  is 100Ω. 
     Moreover, the treatment tool  2  according to Embodiment 1 incorporates a width structure in which a high-frequency electric current flows widthwise across the first and second grasping jaws  8  and  9 . Therefore, the treatment target tissue LT 0  can be limited to a nearly transversely central region of the first and second grasping jaws  8  and  9 . The effect of heat on peripheral tissues that are positioned transversely outside of the first and second grasping jaws  8  and  9  in the periphery of the treatment target tissue LT 0  is thus reduced, allowing the living tissue LT to be treated minimally invasively. 
     In view of the foregoing, the treatment tool  2  according to Embodiment 1 is advantageous in that it is capable of reducing a voltage required to treat a treatment target tissue LT 0  while performing the treatment minimally invasively without reducing the size of the treatment target tissue LT 0 . 
     With the treatment tool  2  according to Embodiment 1, furthermore, the transverse length W 1  of the floating electrode  12  is larger than the spaced distance D 0 . Therefore, the electric resistance value of the floating electrode  12  is secured, making it possible for the floating electrode  12  to serve more reliably as part of the path Pa for the high-frequency electric current. 
     With the treatment tool  2  according to Embodiment 1, in addition, the transversely central position O 1  of the floating electrode  12  is aligned with the transversely central position O 2  between the first and second electrodes  10  and  11 . Consequently, the tissues LT 1  are of the same sizes as each other, and hence can be treated at substantially the same temperatures. The tissue LT 2  that is interposed between the tissues LT 1  can be treated at a uniformly increased temperature by the heat conducted from the tissues LT 1 . Therefore, the treatment target tissue LT 0  can be treated in its entirety in a well-balanced fashion. 
     Embodiment 2 
     Next, Embodiment 2 of the disclosed technology will be described below: 
     The parts of Embodiment 2 which are identical to those of Embodiment 1 described hereinbefore are denoted by identical numeral references, and the description of those parts will be omitted or simplified. 
       FIGS. 9A and 9B  are views illustrating a grasper  7 A of a treatment tool  2 A according to Embodiment 2, and are cross-sectional views corresponding to  FIG. 3 . Specifically,  FIG. 9A  depicts a path for a high-frequency electric current in a former part of a treatment process, whereas  FIG. 9B  depicts a path for a high-frequency electric current in a latter part of the treatment process. 
     The treatment tool  2 A according to Embodiment 2 incorporates a floating electrode  12 A ( FIGS. 9A and 9B ), which is different from the floating electrode  12  of the treatment tool  2  according to Embodiment 1 described hereinbefore, only as to its material. 
     The floating electrode  12 A according to Embodiment 2 is made of a material that is a nonconductor such as a resin or the like with an electrically conductive filler such as carbon, silver, or the like dispersed therein, e.g., an electrically conductive resin such as electrically conductive polyimide, electrically conductive PBI, electrically conductive PEEK, electrically conductive fluororubber, electrically conductive silicon, or the like. If the floating electrode  12 A has a width of 1 mm, for example, then its volume resistivity should appropriately be in the range of approximately 0.1 to 10 Ω·m depending on which target region the living tissue LT is. 
     The electric resistance value of the tissue LT 2  before being treated is 250 S 2 , for example. Furthermore, the electric resistance value of the tissue LT 2  that is in a dry state, i.e., those water content is approximately 20%, is 800 S 2 , for example. In other words, according to Embodiment 2, the electric resistance value 500Ω of the floating electrode  12 A is from a fraction up to substantially the same as, or close to but higher than, the electric resistance value of the tissue LT 2  before being treated, and is lower than the electric resistance value of the tissue LT 2  that is in the dry state. 
     Next, paths for high-frequency electric currents that flow when high-frequency electric power is supplied between the first and second electrodes  10  and  11  while the first and second grasping surfaces  81  and  91  are grasping the living tissue LT therebetween will be described below with reference to  FIGS. 9A and 9B . 
     According to Embodiment 2, as described hereinbefore, the electric resistance value of the floating electrode  12 A is from a fraction up to substantially the same as, or close to but higher than, the electric resistance value of the tissue LT 2  before being treated. Therefore, in the former part of the treatment process, high-frequency electric currents flow between the first and second electrodes  10  and  11  along two paths PaA 1  and PaA 2 , i.e., a path PaA 1  that extends through only the treatment target tissue LT 0 , i.e., the tissues LT 1  and LT 2  and a path PaA 2  that extends through both the tissues LT 1  and the floating electrode  12 A. The high-frequency electric current that flows along the path PaA 1  generates Joule heat in the treatment target tissue LT 0 , whereas the high-frequency electric current that flows along the path PaA 2  generates Joule heat in the tissues LT 1 . 
     The electric resistance value of the treatment target tissue LT 0  goes higher as the treatment of the treatment target tissue LT 0  progresses. As described hereinbefore, the electric resistance value of the floating electrode  12 A is lower than the electric resistance value of the tissue LT 2  in the dry state. In the latter part of the treatment process, therefore, as illustrated in  FIG. 9B , much of the high-frequency electric current flows through the floating electrode  12 A along the path PaA 2 . As the floating electrode  12 A has a higher volume resistivity than the good conductor described in Embodiment 1, the high-frequency electric current that flows through the floating electrode  12 A causes the floating electrode  12 A to function as a tardy heat generator whose temperature rises owing to internal heat generation. In the latter part of the treatment process, therefore, the treatment target tissue LT 0  is treated by being directly heated by the floating electrode  12 A functioning as the tardy heat generator. 
     Embodiment 2 described hereinbefore offers the following advantages as well as the advantages that are the same as those of Embodiment 1: 
     With the treatment tool  2 A according to Embodiment 2, the electric resistance value of the floating electrode  12 A is from a fraction up to substantially the same as, or close to but higher than, the electric resistance value of the tissue LT 2  before being treated, and is lower than the electric resistance value of the tissue LT 2  that is in the dry state. Therefore, the treatment tool  2 A can perform a treatment process in two stages as described hereinbefore. Specifically, in a first stage of treatment ( FIG. 9A ), the tissue LT 2  can also be treated with Joule heat, making the treatment progress fast, compared with Embodiment 1. In a second stage of treatment ( FIG. 9B ), the direct heating by the floating electrode  12 A functioning as the tardy heat generator can further make the treatment progress faster positively. With the conventional structure that is free of the floating electrode  12 A, at the time the electric resistance value of the treatment target tissue LT 0  has increased in excess of the voltage capacity of the power supply, for example, causing the power supply to fail to supply a high-frequency electric current, heating of the treatment target tissue LT 0  cannot be induced. On the other hand, the floating electrode  12 A allows the treatment to continue subsequent to the time referred to hereinbefore, making it possible to strengthen the treatment performance. 
     With the treatment tool  2 A according to Embodiment 2, though the direct heating by the floating electrode  12 A is a contributory factor, the region that is heated by the direct heating is limited within the first and second grasping jaws  8  and  9 . Therefore, even though the direct heating by the floating electrode  12 A is a contributory factor, the effect of heat on peripheral tissues that are positioned transversely outside of the first and second grasping jaws  8  and  9  in the periphery of the treatment target tissue LT 0  is reduced, allowing the living tissue LT to be treated minimally invasively. 
     Embodiment 3 
     Next, Embodiment 3 of the disclosed technology will be described below. 
     The parts of Embodiment 3 which are identical to those of Embodiment 1 described hereinbefore are denoted by identical numeral references, and the description of those parts will be omitted or simplified. 
       FIG. 10  is a view illustrating a grasper  7 B of a treatment tool  2 B according to Embodiment 3. Specifically,  FIG. 10  is a perspective view corresponding to  FIG. 2 . 
     As illustrated in  FIG. 10 , the treatment tool  2 B according to Embodiment 3 incorporates a floating electrode  12 B, which is different from the floating electrode  12  of the treatment tool  2  ( FIG. 2 ) according to Embodiment 1 described hereinbefore, only as to its material. 
       FIG. 11  is a view illustrating the floating electrode  12 B. Specifically,  FIG. 11  is a view of the floating electrode  12 B as viewed from above along the direction normal to the second grasping surface  91 . 
     As illustrated in  FIG. 10 or 11 , the floating electrode  12 B according to Embodiment 3 includes a nonconductor  12 Bi and a thin-film resistance pattern  12 Bp. 
     The nonconductor  12 Bi is made of ceramics such as aluminum nitride, alumina, or the like, or a resin such as polyimide or the like. The nonconductor  12 Bi is of the same shape and size as the floating electrode  12  according to Embodiment 1 described hereinbefore. 
     The thin-film resistance pattern  12 Bp is a portion corresponding to a thin-film resistance body according to the disclosed technology. The thin-film resistance pattern  12 Bp is made of a good conductor such as Pt (Platinum), carbon, SUS (Stainless Steel), or the like, and is formed on an upper surface of the nonconductor  12 Bi by evaporation, sputtering, or the like. 
     According to Embodiment 3, the thin-film resistance pattern  12 Bp is constructed as one line. The thin-film resistance pattern  12 Bp has pads  12 Bp 1  and  12 Bp 2  disposed on one and other ends thereof and facing each other widthwise. The thin-film resistance pattern  12 Bp is substantially 8-shaped, extending from the one end, i.e., the pad  12 Bp 1 , to the other end, i.e., the pad  12 Bp 2 , along the outer edges of the upper surface of the nonconductor  12 Bi. No wiring or the like is added for connection to the pads  12 Bp 1  and  12 Bp 2 . Since it is not clear which longitudinal portions of the first and second grasping jaws  8  and  9  grasp the living tissue LT and what size those portions of the first and second grasping jaws  8  and  9  are during a surgical operation, the pads  12 Bp 1  and  12 Bp 2  are not required to be in the form of a substantially rectangular parallelepiped and to face each other widthwise. Instead, the pads  12 Bp 1  and  12 Bp 2  may have a conductor exposed at one transverse end and may also have a similar structure at the other transverse end. The conductor does not need to be exposed in its entirety, but may be covered with an insulative cover of polyimide or the like except openings defined respectively at the one and other transverse ends. At least one thin-film resistance body or a plurality of thin-film resistance bodies may be included which interconnect the conductors exposed through a pair of openings. A plurality of thin-film resistance bodies may be included which interconnect a plurality of pairs of conductors exposed through a plurality of pairs of openings. The electric resistance values of these thin-film resistance bodies should desirably be in the range of 50 to 500Ω. 
     Paths for high-frequency electric currents that flow when high-frequency electric power is supplied between the first and second electrodes  10  and  11  while the first and second grasping surfaces  81  and  91  are grasping the living tissue LT therebetween will be described below with reference to  FIGS. 12A and 12B . 
       FIGS. 12A and 12B  are cross-sectional views corresponding to  FIG. 3 , and illustrate paths for high-frequency electric currents in former and latter parts of a treatment process. 
     According to Embodiment 3, as described hereinbefore, the electric resistance value of the floating electrode  12 B is from a fraction up to substantially the same as, or close to but higher than, the electric resistance value of the tissue LT 2  before being treated. In a former part of a treatment process, high-frequency electric currents flow between the first and second electrodes  10  and  11  along two paths PaB 1  and PaB 2 , i.e., along a path PaB 1  that extends through only the treatment target tissue LT 0 , i.e., the tissues LT 1  and LT 2 , and a path PaB 2  that extends through the tissues LT 1  and the floating electrode  12 B. The path PaB 2  has a path PaB 3  that extends through the tissue LT 2 , but not through the thin-film resistance pattern  12 Bp, and a path PaB 4  ( FIG. 11 ) that extends through the thin-film resistance pattern  12 Bp. In other words, the high-frequency electric currents that flow along the paths PaB 1  and PaB 2  generate Joule heat in the tissues LT 1  and LT 2 , i.e., the treatment target tissue LT 0 . 
     As the treatment of the treatment target tissue LT 0  progresses and the impedance of the tissue LT 2  increases, the paths PaB 1  and PaB 3  become less likely to occur, but the paths PaB 2  and PaB 4  become essentially dominant. In other words, in a latter part of the treatment process, since the high-frequency electric current flows in the thin-film resistance pattern  12 Bp along the path PaB 4 , the thin-film resistance pattern  12 Bp functions as a tardy heat generator whose temperature rises owing to internal heat generation. Therefore, the treatment target tissue LT 0  is treated by being directly heated by the floating electrode  12 B functioning as the tardy heat generator. 
     Embodiment 3 described hereinbefore offers the following advantages as well as the advantages that are the same as those of Embodiment 2: 
     With the treatment tool  2 B according to Embodiment 3, inasmuch as the resistance body that has had guaranteed reliability can be used without wiring, a heat-generating region can freely be configured by the shape and resistance density of the thin-film resistance pattern  12 Bp. If a resistance body is used as a heater, then two wires are required for connection to the resistance body. Since such wires are not required, the second grasping jaw  9  can be reduced in size, i.e., the grasper  7 B can be reduced in diameter. 
     Embodiment 4 
     Embodiment 4 of the disclosed technology will be described below. 
     The parts of Embodiment 4 which are identical to those of Embodiment 1 described hereinbefore are denoted by identical numeral references, and the description of those parts will be omitted or simplified. 
       FIG. 13  is a view illustrating a grasper  7 C of a treatment tool  2 C according to Embodiment 4. Specifically,  FIG. 13  is a cross-sectional view corresponding to  FIG. 3 . 
     As illustrated in  FIG. 13 , the treatment tool  2 C according to Embodiment 4 is different from the treatment tool  2  ( FIG. 3 ) according to Embodiment 1 described hereinbefore, as to the position where a floating electrode is disposed. 
     In the second grasping jaw  9  according to Embodiment 4, the second grasping surface  91  is free of the floating electrode  12 , as illustrated in  FIG. 13 . Though the second grasping surface  91  according to Embodiment 4 is free of the floating electrode  12 , the second grasping surface  91  has a flat shape as with Embodiment 1. The second grasping surface  91  may be coated with an electrically insulative coating material which is non-adhesive to living bodies as described hereinbefore in Embodiment 1. 
     In the first grasping jaw  8  according to Embodiment 4, the first grasping surface  81  includes a floating electrode  12 C in addition to the first and second electrodes  10  and  11 . 
     The floating electrode  12 C is made of the same material as the floating electrode  12  described hereinbefore in Embodiment 1. The floating electrode  12 C has the same shape, size, and function, i.e., the function as part of the path for the high-frequency electric current between the first and second electrodes  10  and  11 , as the floating electrode  12 . 
     The floating electrode  12 C is embedded in an area of the first grasping surface  81  that is positioned centrally widthwise, and extends the entire length of the first grasping surface  81 . The floating electrode  12 C serves as part of the first grasping surface  81 . The first grasping surface  81  according to Embodiment 4, though the floating electrode  12 C is embedded therein, is shaped flatwise as with Embodiment 1 described hereinbefore. The lower surface of the floating electrode  12 C as illustrated in  FIG. 13  may be coated with an electrically conductive coating material which is non-adhesive to living bodies as described hereinbefore in Embodiment 1. 
     In Embodiment 4, the positional relationship of the first and second electrodes  10  and  11  and the floating electrode  12 C as viewed along the directions in which the first and second grasping surfaces  81  and  91  face each other when the grasper  7 C is in the closed state is the same as Embodiment 1. The spaced distance D 1  between the first electrode  10  and the floating electrode  12 C, i.e., the spaced distance D 2  between the second electrode  11  and the floating electrode  12 C, is set to be longer than the spaced distance D 0  ( FIG. 13 ). 
     The floating electrode  12 C is not limited to the shape of the plate, but may be of a different shape such as a round rod or the like embedded such that it may have a protrusive portion that is small compared with the distance between the first and second grasping jaws  8  and  9 . The floating electrode  12 C may not necessarily be made of a bulk material, but may be made of a foil or thin film of a good conductor or an electrically conductive DLC thin film or the like that is formed by CVD or the like. 
     Next, a path for a high-frequency electric current that flows when high-frequency electric power is supplied between the first and second electrodes  10  and  11  while the first and second grasping surfaces  81  and  91  are grasping the living tissue LT therebetween will be described below with reference to  FIG. 13 . 
     The floating electrode  12 C according to Embodiment 4 is made of a good conductor as with the floating electrode  12  described hereinbefore in Embodiment 1. Therefore, as illustrated in  FIG. 13 , a high-frequency electric current flows between the first and second electrodes  10  and  11  mainly along a path PaC that extends through the tissues LT 1  and the floating electrode  12 C. In other words, as with Embodiment 1, each of the tissues LT 1  is treated by Joule heat. The tissue LT 2  is treated by heat conduction from the Joule heat generated in each of the tissues LT 1 . 
     Embodiment 4 described hereinbefore offers the following advantages as well as the advantages that are the same as those of Embodiment 1: 
     With the treatment tool  2 C according to Embodiment 4, the first grasping jaw  8  includes the first and second electrodes  10  and  11  and the floating electrode  12 C. Stated otherwise, the second grasping jaw  9  does not have any of the first and second electrodes  10  and  11  and the floating electrode  12 C. Therefore, the second grasping jaw  9  can be simplified in structure and can be reduced in size, i.e., the grasper  7 C can be reduced in diameter. 
     With the treatment tool  2 C according to Embodiment 4, the spaced distance D 1  between the first electrode  10  and the floating electrode  12 C, i.e., the spaced distance D 2  between the second electrode  11  and the floating electrode  12 C, is set to be longer than the spaced distance D 0 . If the spaced distance D 1  or D 2  is shorter than the spaced distance D 0 , then it is difficult for the path PaC for the high-frequency electric current to reach the interface between tissues to be joined, such as of a lumen, a blood vessel, or the like. However, as the spaced distance D 1  or D 2  is longer than the spaced distance D 0 , the path PaC for the high-frequency electric current can extend deeply thicknesswise to the tissue interface. Accordingly, the treatment can be effectively performed. 
     Embodiment 5 
     Embodiment 5 of the disclosed technology will be described below. 
     The parts of Embodiment 5 which are identical to those of Embodiment 4 described hereinbefore are denoted by identical numeral references, and the description of those parts will be omitted or simplified. 
       FIG. 14  is a view illustrating a grasper  7 D of a treatment tool  2 D according to Embodiment 5. Specifically,  FIG. 14  is a cross-sectional view corresponding to  FIG. 13 . 
     As illustrated in  FIG. 14 , the treatment tool  2 D according to Embodiment 5 is different from the treatment tool  2 C ( FIG. 13 ) according to Embodiment 4 described hereinbefore, as to the number of floating electrodes. 
     As illustrated in  FIG. 14 , the first grasping surface  81  according to Embodiment 5 has a plurality of, or two in Embodiment 5, floating electrodes  12 D in addition to the first and second electrodes  10  and  11 . 
     The two floating electrodes  12 D are made of the same material as the floating electrode  12 C described hereinbefore in Embodiment 4 and have the same shape, size, and function as the floating electrode  12 C. 
     The floating electrodes  12 D are embedded in respective areas of the first grasping surface  81  that is positioned between the first and second electrodes  10  and  11 , and extends the entire length of the first grasping surface  81 . More specifically, the floating electrodes  12 D are disposed such that the distance between one of the floating electrodes  12 D and the first electrode  10  adjacent thereto, the distance between the other floating electrode  12 D and the second electrode  10  adjacent thereto, and the distance between the floating electrodes  12 D are equal to each other. A transversely central position O 1  between the two floating electrodes  12 D is aligned with a transversely central position O 2  between the first and second electrodes  10  and  11 . These floating electrodes  12 D serve as part of the first grasping surface  81 . The first grasping surface  81  according to Embodiment 5, though the two floating electrodes  12 D are embedded therein, is shaped flatwise as with Embodiment 4 described hereinbefore. The lower surfaces of the two floating electrodes  12 D in the first grasping surface  81  as illustrated in  FIG. 14  may be coated with an electrically conductive coating material which is non-adhesive to living bodies as described hereinbefore in Embodiment 4. 
     The number of the floating electrodes  12 D is not limited to two, but may be three or more. Each of the floating electrodes  12 D is not limited to the shape of the plate, but may be of a different shape such as a round rod or the like embedded such that it may have a protrusive portion that is small compared with the distance between the first and second grasping jaws  8  and  9 . The floating electrodes  12 D may not necessarily be made of a bulk material, but may be made of a foil or thin film of a good conductor or an electrically conductive DLC thin film or the like that is formed by CVD or the like. 
     Next, a path for a high-frequency electric current that flows when high-frequency electric power is supplied between the first and second electrodes  10  and  11  while the first and second grasping surfaces  81  and  91  are grasping the living tissue LT therebetween will be described below with reference to  FIG. 14 . 
     In the living tissue LT that is grasped by the first and second grasping surfaces  81  and  91 , as viewed along the directions in which the first and second grasping surfaces  81  and  91  face each other, a tissue positioned between the two floating electrodes  12 D will hereinafter be referred to as a tissue LT 1 D ( FIG. 14 ), and tissues positioned between the tissues LT 1  and LT 1 D as tissues LT 2 D ( FIG. 14 ). 
     According to Embodiment 5, as described hereinbefore, the two floating electrodes  12 D are uniformly spaced between the first and second electrodes  10  and  11 . Therefore, when high-frequency electric power is supplied between the first and second electrodes  10  and  11 , the two floating electrodes  12 D are kept at uniformly assigned potentials between the potentials of the first and second electrodes  10  and  11 . The two floating electrodes  12 D are made of a good conductor as with the floating electrode  12 C described hereinbefore in Embodiment 4. Therefore, as illustrated in  FIG. 14 , a high-frequency electric current flows between the first and second electrodes  10  and  11  mainly along a path PaD that extends through the tissues LT 1  and LT 1 D and the floating electrode  12 D. Thus, the tissue LT 1 D as well as the tissues LT 1  is treated by Joule heat. The tissues LT 2 D are treated by heat conduction from the Joule heat generated in each of the tissues LT 1  and LT 1 D. In other words, each of the tissues LT 1 , LT 1 D, and LT 2 D is a treatment target tissue LT 0  to be treated. 
     Embodiment 5 described hereinbefore offers the following advantages as well as the advantages that are the same as those of Embodiment 4: 
     The treatment tool  2 D according to Embodiment 5 has the two floating electrodes  12 D. Therefore, the combined resistance between the first and second electrodes  10  and  11  can further be reduced. There are available more tissues LT 1  where Joule heat is generated, i.e., more heat-generating spots, making it possible to treat the treatment target tissue LT 0  more uniformly. 
     Embodiment 6 
     Embodiment 6 of the disclosed technology will be described below. 
     The parts of Embodiment 6 which are identical to those of Embodiment 4 described hereinbefore are denoted by identical numeral references, and the description of those parts will be omitted or simplified. 
       FIG. 15  is a view illustrating a grasper  7 E of a treatment tool  2 E according to Embodiment 6. Specifically,  FIG. 15  is a view illustrating the first grasping surface  81  of the first grasping jaw  8 . 
     As illustrated in  FIG. 15 , the treatment tool  2 E according to Embodiment 6 is different from the treatment tool  2 C ( FIG. 13 ) according to Embodiment 4 described hereinbefore, as to the number of floating electrodes. 
     As illustrated in  FIG. 15 , the first grasping surface  81  according to Embodiment 6 has a plurality of, or twenty in Embodiment 5, floating electrodes  12 E in addition to the first and second electrodes  10  and  11 . 
     The twenty floating electrodes  12 E are made of the same material as the floating electrode  12 C described hereinbefore in Embodiment 4 and have the same shape, size, and function as the floating electrode  12 C. 
     The floating electrodes  12 E are identical in shape. Each of the floating electrodes  12 E has a longitudinal dimension smaller than the floating electrode  12 C described hereinbefore in Embodiment 4. The floating electrodes  12 E are embedded in the first grasping surface  81  such that they are positioned between the first and second electrodes  10  and  11  and juxtaposed along the longitudinal directions. More specifically, each of the floating electrodes  12 E has a transversely central position O 1  that is aligned with a transversely central position O 2  between the first and second electrodes  10  and  11 . The floating electrodes  12 E serve as part of the first grasping surface  81 . The first grasping surface  81  according to Embodiment 6, though the floating electrodes  12 E are embedded therein, is shaped flatwise as with Embodiment 4 described hereinbefore. The lower surfaces of the twenty floating electrodes  12 E in the first grasping surface  81  as illustrated in  FIG. 15  may be coated with an electrically conductive coating material which is non-adhesive to living bodies as described hereinbefore in Embodiment 4. 
     The number of the floating electrodes  12 E is not limited to twenty, but may be any other number insofar as it is two or more. Each of the floating electrodes  12 E is not limited to the plate, but may be of a different shape such as a round rod or the like embedded such that it may have a protrusive portion that is small compared with the distance between the first and second grasping jaws  8  and  9 . The floating electrodes  12 E may not necessarily be made of a bulk material, but may be made of a foil or thin film of a good conductor or an electrically conductive DLC thin film or the like that is formed by CVD or the like. 
     Next, paths for high-frequency electric current that flow when high-frequency electric power is supplied between the first and second electrodes  10  and  11  while the first and second grasping surfaces  81  and  91  are grasping the living tissue LT therebetween will be described below with reference to  FIG. 15 . 
     In the living tissue LT that is grasped by the first and second grasping surfaces  81  and  91 , as viewed along the directions in which the first and second grasping surfaces  81  and  91  face each other, tissues positioned between the twenty floating electrodes  12 E will hereinafter be referred to as tissues LT 1 E ( FIG. 15 ), and tissues positioned between the tissues LT 1 E as tissues LT 2 E ( FIG. 15 ). 
     According to Embodiment 6, there are a plurality of floating electrodes  12 E and they are made of a good conductor, as with Embodiment 5 described hereinbefore. Therefore, as with Embodiment 5 described hereinbefore, between the first and second electrodes  10  and  11 , a high-frequency electric current flows mainly between the first electrode  10  and the floating electrodes  12 E, between the second electrode  11  and the floating electrodes  12 E, and between the floating electrodes  12 E. Thus, the tissue LT 1 E as well as the tissues LT 1  are treated by Joule heat. The tissues LT 2 E are treated by heat conduction from the Joule heat generated in each of the tissues LT 1  and LT 1 E. In other words, each of the tissues LT 1 , LT 1 E, and LT 2 E is a treatment target tissue LT 0  to be treated. 
     Embodiment 6 described hereinbefore offers the following advantages as well as the advantages that are the same as those of Embodiment 5: 
     The treatment tool  2 E according to Embodiment 6 has the twenty floating electrodes  12 E juxtaposed along the longitudinal directions. Therefore, it is possible to make the intervals between the first and second electrodes  10  and  11  and the floating electrodes  12 E wide, resulting in an electrically stable structure, compared with Embodiment 5 described hereinbefore. 
     The floating electrodes  12 E are small discrete electrodes compared with Embodiments 1 and 4 according to which the floating electrodes  12  and  12 C extend the entire length in the longitudinal directions. If the floating electrodes  12 E are used as a tardy heat generator described hereinbefore in Embodiment 2, then they can avoid heat dissipation from themselves. On the other hand, heat is likely to dissipate from the larger floating electrodes  12  and  12 C when used as a tardy heat generator. 
     Though the combined resistance between the first and second electrodes  10  and  11  is high compared with Embodiments 1 and 3 described hereinbefore, the combined resistance can be adjusted by using a material having a small volume resistivity as the floating electrodes  12 E. 
     Embodiment 7 
     Embodiment 7 of the disclosed technology will be described below. 
     The parts of Embodiment 7 which are identical to those of Embodiments 1 and 3 described hereinbefore are denoted by identical numeral references, and the description of those parts will be omitted or simplified. 
       FIG. 16  is a view illustrating a grasper  7 F of a treatment tool  2 F according to Embodiment 7. Specifically,  FIG. 16  is a cross-sectional view corresponding to  FIGS. 3 and 13 . 
     As illustrated in  FIG. 16 , the treatment tool  2 F according to Embodiment 7 is different from the treatment tool  2  ( FIG. 3 ) according to Embodiment 1 described hereinbefore and the treatment tool  2 C ( FIG. 13 ) according to Embodiment 4 described hereinbefore, as to the number of floating electrodes. Specifically, as illustrated in  FIG. 16 , the grasper  7 F according to Embodiment 7 includes in combination the first grasping jaw  8  having the first and second electrodes  10  and  11  and the floating electrode  12 C described hereinbefore in Embodiment 4 and the second grasping jaw  9  having the floating electrode  12  described hereinbefore in Embodiment 1. 
     Next, paths for high-frequency electric currents that flow when high-frequency electric power is supplied between the first and second electrodes  10  and  11  while the first and second grasping surfaces  81  and  91  are grasping the living tissue LT therebetween will be described below with reference to  FIG. 16 . 
     In the living tissue LT that is grasped by the first and second grasping surfaces  81  and  91 , a tissue positioned between the two floating electrodes  12  and  12 C will hereinafter be referred to as a tissue LT 1 F ( FIG. 16 ). 
     According to Embodiment 7, there are two floating electrodes  12  and  12 C and they are made of a good conductor, as with Embodiment 5 described hereinbefore. Therefore, as with Embodiment 5 described hereinbefore, between the first and second electrodes  10  and  11 , high-frequency electric currents flow mainly between the first and second electrodes  10  and  11  and the floating electrode  12 C, i.e., along a path PaF 1 , between the first and second electrodes  10  and  11  and the floating electrode  12 , i.e., along a path PaF 2 , and between the floating electrodes  12  and  12 C, i.e., along a path PaF 3 . Thus, the tissue LT 1 F as well as the tissues LT 1  is treated by Joule heat. Each of the tissues LT 1  and LT 1 F is a treatment target tissue LT 0  to be treated. 
     The treatment tool  2 F according to Embodiment 7 described hereinbefore offers the following advantages as well as the advantages that are the same as those of Embodiment 5: 
     With the treatment tool  2 F according to Embodiment 7, the floating electrode  12 C is disposed in the first grasping surface  81 , whereas the floating electrode  12  is disposed in the second grasping surface  91 . In each of the tissues LT 1 , Joule heat is generated on the first grasping surface  81  side by the high-frequency electric current flowing along the path PaF 1 , and Joule heat is generated on the second grasping surface  91  side by the high-frequency electric current flowing along the path PaF 2 . In other words, the tissues LT 1  can be treated more uniformly. The tissue LT 1 F interposed between the tissues LT 1  can be treated by Joule heat generated by the high-frequency electric current flowing along the path PaF 3 . Therefore, the progress of the treatment is made faster. 
     Other Embodiments 
     The embodiments of the disclosed technology have been described hereinbefore. However, the disclosed technology should not be limited to Embodiments 1 through 7 described hereinbefore. 
     In Embodiments 1 through 7 described hereinbefore, the first grasping jaw  8  is disposed upwardly of the second grasping jaw  9 . However, the disclosed technology is not limited to such a structure. Instead, the first grasping jaw  8  may be disposed downwardly of the second grasping jaw  9 . The shaft  6  or the grasper  7 , i.e.,  7 A through  7 F, may be made rotatable about the central axis of the shaft  6  with respect to the handle  5 . 
     In Embodiments 1 through 7 described hereinbefore, the first and second grasping surfaces  81  and  91  are flat surfaces. The disclosed technology is not limited to such a structure. Instead, the first and second grasping surfaces  81  and  91  may be shaped otherwise for the purpose of increasing the treatment performance. For example, one of the first and second grasping surfaces  81  and  91  may be of a flat shape, whereas the other may be of a protrusion shape. Alternatively, one of the first and second grasping surfaces  81  and  91  may be of a protrusion shape, whereas the other may be of a recess shape. For effectively making an incision in the living tissue LT as a treatment process, at least one of the first and second grasping surfaces  81  and  91  may have a portion having a V-shaped cross section at the incising position in the vicinity of the other grasping surface. 
     In Embodiments 1 through 7 described hereinbefore, the two electrodes, i.e., the first and second electrodes  10  and  11 , are employed for imparting high-frequency energy. However, the number of such electrodes is not limited to two, but may be three or more. 
     In Embodiments 1 through 7 described hereinbefore, the positions where the first and second electrodes  10  and  11  and the floating electrode  12 , i.e.,  12 A through  12 E, are not limited to the positions described hereinbefore in Embodiments 1 through 7. Insofar as the floating electrode  12 , i.e.,  12 A through  12 E, is disposed between the first and second electrodes  10  and  11  as viewed along the directions in which the first and second grasping surfaces  81  and  91  face each other when the grasper is in the closed state, the electrodes may be disposed in other positions. For example, while the first and second electrodes  10  and  11  are disposed in the first grasping surface  81 , i.e., in one grasping surface, according to Embodiments 1 through 7 described hereinbefore, the first and second electrodes  10  and  11  may be disposed in different grasping surfaces, respectively. 
     In Embodiments 1 through 7 described hereinbefore, the treatment tool  2 , i.e.,  2 A through  2 F, treats the living tissue LT by imparting high-frequency energy thereto. The disclosed technology is not limited to such a process. Instead, the treatment tool  2  may treat the living tissue LT by imparting thermal energy, ultrasonic energy, or optical energy such as laser or the like, other than high-frequency energy, to the living tissue LT. 
     In Embodiments 4 through 7 described hereinbefore, the floating electrodes  12 C through  12 E are made of a good conductor. However, they are not limited to such a material. Instead, as with the floating electrode  12 A described hereinbefore in Embodiment 2 and the floating electrode  12 B described hereinbefore in Embodiment 3, the floating electrodes  12 C through  12 E may be made of an electrically conductive resin or a nonconductor and a thin-film resistance pattern, thereby making themselves into a tardy heat generator. 
     In sum, one aspect of the disclosed technology is directed to a treatment tool comprises a first grasping jaw having a first grasping surface. A second grasping jaw having a second grasping surface and is configured to engage with the first grasping jaw so as to relatively pivot with respect to one another for holding a living tissue therebetween. A first electrode is disposed on the first grasping surface. A second electrode is disposed on either the first grasping surface or the second grasping surface and is configured to generate high-frequency energy in tandem with the first electrode to the living tissue held therebetween. A floating electrode is disposed in at least one of the first grasping surface and the second grasping surface. The floating electrode having a first end and a second end. Both of the first end and second end is disposed between the first electrode and the second electrode as viewed along directions in which the first grasping surface and the second grasping surface face each other when the first grasping surface and the second grasping surface face each other. 
     The floating electrode has an electric resistance value lower than the electric resistance value of the living tissue. The floating electrode has an electric resistance value lower than the electric resistance value of the living tissue in a dry state. The floating electrode has at least one electrically exposed area on one end thereof on a first electrode side and an opposed end thereof on a second electrode side. The floating electrode including at least one thin-film resistance body interconnecting the area on the one end and the area on the opposed end. The second electrode and the floating electrode are disposed in the first grasping surface. Each of spaced distance between the first electrode and the floating electrode and spaced distance between the second electrode and the floating electrode is longer than spaced distance between the first grasping surface and the second grasping surface when the first grasping surface and the second grasping surface hold the living tissue therebetween. The floating electrode has a length longer than spaced distance between the first grasping surface and the second grasping surface as viewed along longitudinal directions of the first grasping surface and the second grasping surface when the first grasping surface and the second grasping surface are in contact with one another. The floating electrode is defined by a plurality of the floating electrodes. The plurality of floating electrodes are disposed in one of the first grasping surface and the second grasping surface or both of the respective first and second grasping surfaces. The plurality of floating electrodes are disposed in each of the first grasping surface and the second grasping surface. The floating electrode has a central position aligned with a central position between the first electrode and the second electrode as viewed along the directions in which the first grasping surface and the second grasping surface face each other when the first grasping surface and the second grasping surface face each other. 
     Another aspect of the disclosed technology is directed to a treatment system used for treatment of a body tissue by applying electrical energy thereto. The treatment system comprises a controller and a treatment tool configured to be attached to controller. The treatment tool comprises a shaft having a first end and a second end. A handle is attached to the first end. Respective first and second grasping jaws each of which having respective first and second grasping surfaces configured to be engaged with the second end of the shaft so as to pivot with respect to one another for holding living tissue therebetween during the treatment. A first electrode is disposed on the first grasping surface. A second electrode is disposed on either the first grasping surface or the second grasping surface and is configured to generate high-frequency energy in tandem with the first electrode to the living tissue being held therebetween. At least one floating electrode is disposed in at least one of the respective first and second grasping surfaces so that the treatment tool being capable of reducing a voltage required to treat the body tissue while performing the treatment without reducing a size of the body tissue. 
     The floating electrode has an electric resistance value lower than the electric resistance value of the living tissue. The floating electrode becomes part of a path of high-frequency electric current when body tissue is grasped by the respective first and grasping jaws so as to reduce resistance between the respective first and second electrodes. The floating electrode is electrically communicating with the respective first and second electrodes without being connected to the controller. The floating electrode is defined by a plurality of the floating electrodes. 
     While various embodiments of the disclosed technology have been described above, it should be understood that they have been presented by way of example only, and not of limitation. Likewise, the various diagrams may depict an example schematic or other configuration for the disclosed technology, which is done to aid in understanding the features and functionality that can be included in the disclosed technology. The disclosed technology is not restricted to the illustrated example schematic or configurations, but the desired features can be implemented using a variety of alternative illustrations and configurations. Indeed, it will be apparent to one of skill in the art how alternative functional, logical or physical locations and configurations can be implemented to implement the desired features of the technology disclosed herein. 
     Although the disclosed technology is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations, to one or more of the other embodiments of the disclosed technology, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus, the breadth and scope of the technology disclosed herein should not be limited by any of the above-described exemplary embodiments. 
     Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term “including” should be read as meaning “including, without limitation” or the like; the term “example” is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; the terms “a” or “an” should be read as meaning “at least one”, “one or more” or the like; and adjectives such as “conventional”, “traditional”, “normal”, “standard”, “known” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, where this document refers to technologies that would be apparent or known to one of ordinary skill in the art, such technologies encompass those apparent or known to the skilled artisan now or at any time in the future. 
     The presence of broadening words and phrases such as “one or more”, “at least”, “but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent. 
     Additionally, the various embodiments set forth herein are described in terms of exemplary schematics, block diagrams, and other illustrations. As will become apparent to one of ordinary skill in the art after reading this document, the illustrated embodiments and their various alternatives can be implemented without confinement to the illustrated examples. For example, block diagrams and their accompanying description should not be construed as mandating a particular configuration. 
     NUMERAL REFERENCE LIST 
     
         
         
           
               1  Treatment system 
               2 ,  2 A to  2 F Treatment tool 
               3  Controller 
               4  Foot switch 
               5  Handle 
               6  Shaft 
               7 ,  7 A to  7 F Grasper 
               8 ,  9  First, second grasping jaw 
               10 ,  11  First, second electrode 
               12 ,  12 A to  12 E Floating electrode 
               12 Bi Nonconductor 
               12 Bp Thin-film resistance pattern 
               12 Bp 1 ,  12 Bp 2  Pad 
               51  Manipulating knob 
               81 ,  91  First, second grasping surface 
             C Electric cable 
             D 0  to D 2  Spaced distance 
             LT Living tissue 
             LT 0  Treatment target tissue 
             LT 1 , LT 1 D to LT 1   f , LT 2 , LT 2 D, LT 2 E Tissue 
             O 1 , O 2  Central position 
             Pa, PaA 1 , PaA 2 , PaB 1  to PaB 4 , PaC, PaD, PaF 1  to PaF 3  Path 
             R 1  Arrow 
             W 1  Length