Abstract:
A medical device includes a portion which is expected to be subjected to an irreversible structural change due to an air pressure difference when the medical device is placed in a negative pressure in a sterilizing process. By the irreversible change of the aforementioned portion, an alarm display is exposed, or at least part of a function of the device is restricted or use of at least part of the function of the device is disabled.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-226007, filed Aug. 2, 2004, the entire contents of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a medical device. More specifically, the present invention relates to preventing reuse of a single use medical device.  
         [0004]     2. Description of the Related Art  
         [0005]     In recent years, disposable medical devices, or single use medical devices (Single use Devices=SUD) are being used in the medical field. The disposable medical device or the single use medical device (hereinafter, referred simply as SUD medical device) can prevent infection diseases or the like by being discarded after each use for a treatment and replaced with a new SUD medical device for each treatment. Durability such as strength and required quality such as performance of the SUD medical devices are set to certain degrees on the premise of a single use.  
         [0006]     While reusable medical devices are reused after being washed, disinfected, and sterilized to prevent cross infection among patients, the SUD medical devices are not manufactured on the assumption of reuse. Therefore, reuse of the SUD medical devices must be avoided.  
         [0007]     Medical devices for preventing reuse of the SUD medical devices after a single use are proposed, for example, in Japanese Patent No. 2730990, JP-UM-A-3-101908, and JP-B-7-79839. In these patent publications, a medical introduction tube for introducing an instrument such as a catheter into a body cavity or a plug member provided at a pipe sleeve of an instrument insertion channel provided on an endoscope are disclosed. The plug member is provided to prevent blood or sewage in the body cavity from flowing back through the pipe sleeve of the medical introduction tube or the instrument insertion channel of the endoscope. The plug member includes a finger hook portion for hooking a finger when removing the plug member after being mounted to the pipe sleeve and used, and a breakable portion for causing the plug member to be broken from the finger hook portion when the finger hook portion is pulled, so as to be broken at the breakable portion when the finger hook portion is pulled to prevent reuse. In this manner, part of the plug member is adapted to be broken irreversibly to prevent the plug member from again being mounted to the pipe sleeve.  
         [0008]     In JP-A-5-38324, a disposable type endoscope is provided with a pressure breakable portion (thinned portion), which is adapted to be broken when a pressure difference between the inside and the outside exceeds a predetermined pressure at an insertion portion of the endoscope. This device is adapted to be broken partly at the insertion portion when it cannot sustain the pressure difference between the inside and the outside of the endoscope stored in a chamber utilizing a property that inside the chamber is brought into a negative pressure at the time of ethylene oxide gas sterilization (referred to simply as EOG sterilization hereinafter), thereby preventing reuse of the device.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     Accordingly, it is an object of the invention to provide a versatile reuse prevention technology in disposable medical devices.  
         [0010]     A medical device according to the invention is provided with a portion which is expected to be subjected to irreversible structural change due to a pressure difference when the medical device is placed under a negative pressure in a process of sterilization. The device can be adapted to display a warning, or to restrict or disable at least part of the function thereof when such an irreversible change occurs at the aforementioned portion.  
         [0011]     As the part which is expected to be subjected to the irreversible structural change due to the pressure difference, for example, an air chamber may be provided. The air chamber can be specifically used for this purpose only, without having other intended uses. In this arrangement, part of the medical device other than the air chamber can be manufactured with a required strength. When the air chamber has other intended uses, the medical device may easily be fragile at a position of the air chamber.  
         [0012]     For example, the air chamber may include a recess which has an indication of “Do not use” on an interior surface thereof and a partitioning wall which seals the interior of the recess at the same pressure as the ambient pressure, and is adapted to be separated (or broken) when a difference between the ambient pressure and the atmospheric pressure around the medical device is greater than a predetermined value, such as when the atmospheric pressure becomes negative.  
         [0013]     The recess may be provided at a part of a member which constitutes the medical device, or on a tag member of the medical device. The partitioning wall may be opaque. The opaque partitioning wall is advantageous since the indication of “Do not use” is not visible until the partitioning wall is separated or broken.  
         [0014]     The part which is expected to be subjected to the irreversible structural change due to the pressure difference may be configured of a notch for causing an operating unit to be broken when a force exceeding a predetermined magnitude is applied to the operating unit, and a cover member mounted to a peripheral edge of the notch for preventing breakage of the operating unit from the notch and adapted to be separated when a difference between the ambient pressure and the atmospheric pressure around the medical device is greater than a predetermined value, such as when the atmospheric pressure becomes negative.  
         [0015]     Furthermore, the part which is expected to be subjected to the irreversible structural change due to the pressure difference may be configured of a function restricting module provided on the operating unit of the medical device held and operated by an operator, so that an irreversible operation is achieved by an action of the pressure when a difference between the ambient pressure and the atmospheric pressure around the medical device is greater than a predetermined value, such as when the atmospheric pressure becomes negative. When the pressure difference is greater than the predetermined value, the function restricting module acts to restrict an operative function of the operating unit. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0016]     These and other features, aspects, and advantages of the apparatus and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:  
         [0017]      FIG. 1  is a plan view showing a general structure of a disposable medial device according to a first embodiment;  
         [0018]      FIG. 2  is an explanatory cross-sectional view of a recess and a partitioning wall provided on an operating unit of the disposable medical device as taken along section line  2 - 2  in  FIG. 1 ;  
         [0019]      FIG. 3  is a cross-sectional view showing a state in which the partitioning wall of  FIG. 2  is separated from the recess provided on the operating unit of the disposable medical device;  
         [0020]      FIG. 4  is an explanatory drawing showing an indication that reuse is prohibited provided in the recess of the disposable medical device;  
         [0021]      FIG. 5  is an explanatory drawing showing another application of the disposable medical device according to the first embodiment;  
         [0022]      FIG. 6  is a perspective view showing a general structure of a disposable medical device according to a second embodiment;  
         [0023]      FIG. 7  is a cross-sectional view showing a structure of a holding portion of the operating unit of the disposable medical device of  FIG. 6 ;  
         [0024]      FIG. 8  is a plan view showing an action of the operating unit of  FIG. 7 ;  
         [0025]      FIG. 9  is a cross-sectional view showing a structure of the function restricting module to be used in a disposable medical device according to a third embodiment;  
         [0026]      FIG. 10  is a cross-sectional view showing an operating state of the function restricting module of  FIG. 9 ;  
         [0027]      FIG. 11  is an explanatory drawing explaining an example in which the function restricting module of  FIG. 9  is used in holding forceps;  
         [0028]      FIG. 12  is an explanatory drawing showing an example in which the function restricting module of  FIG. 9  is used in a trocar; and  
         [0029]      FIG. 13  is an explanatory drawing showing an example in which the function restricting module of  FIG. 9  is used in displacement forceps. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     Preferred embodiments are described below with reference to the accompanying drawings.  
         [0031]     Referring now to  FIG. 1  to  FIG. 5 , a medical device according to a first embodiment will be described.  
         [0032]     In the first embodiment, holding forceps used in an endoscopic operation, which is a surgical operation conducted for an affected part while observing inside of the body cavity by an endoscope, will be described as an example of the medical device. The holding forceps  1  includes an insertion portion  2  and an operating unit  3  as shown in  FIG. 1 . The insertion portion  2  is inserted into a body cavity via a trocar, not shown, and a holding member  4  is provided at an extremity of the insertion portion  2 . The holding member  4  is used for holding tissue of an affected part in the body cavity, and is remotely opened and closed using a holding wire, not shown, disposed in the insertion portion  2 . The operating unit  3  includes a holding portion  6  formed into a shape like a gun grip and gripped by a hand of an operator, and a handle  5  operated by a finger of the operator who grips the holding portion  6 . The handle  5  includes a holding wire connected thereto for operating the holding member  4 , so that the holding member  4  opens or closes by moving the handle  5  in the direction indicated by Arrow A in  FIG. 1 .  
         [0033]     A recess  7  covered by a partitioning wall member  9  is provided on one side of the holding portion  6  of the operating unit  3  of the holding forceps  1 . The recess  7  covered by the partitioning wall member  9  is formed to have a predetermined depth from a surface of the holding portion  6  as shown in  FIG. 2 . A peripheral edge portion  8  to which the periphery of the partitioning wall member  9  is fixed by an adhesive agent is formed on the peripheral edge of the recess  7 . The recess  7  can have any shape, such as a circular, oval or rectangular shape. As shown in  FIG. 4 , the recess includes a reuse prohibiting indication such as “Do not reuse!” as shown in  FIG. 4  or “Reuse is prohibited” which is not shown in the drawings.  
         [0034]     An air chamber  10  is defined by the partitioning wall member  9  fixed to the peripheral edge portion  8  of the recess  7  by an adhesive agent, for example a silicon adhesive agent. In other words, when manufacturing the holding forceps  1 , a sterilizing process such as gamma ray sterilization or electron beam sterilization of SUD medical devices is conducted under an atmospheric pressure and, in the process of the sterilization, the partitioning wall member  9  is adhered and fixed to the peripheral edge portion  8  of the recess  7  to seal sterilized air at an ambient pressure in the air chamber  10  inside the recess  7 .  
         [0035]     The partitioning wall member  9  is adhered and fixed so as to prevent the air in the air chamber  10  in the recess  7  from leaking out under an ambient pressure, and be separated easily when an atmospheric air pressure outside the air chamber  10  becomes significantly less than a pressure inside the air chamber  10 , such as when the atmospheric pressure becomes negative, indicating that the holding forceps  1  is being sterilized (which is prohibited).  
         [0036]     In this manner, the holding forceps  1  sterilized by sterilization process during manufacture of the SUD medical devices is sealed in a sterilized bag and presented to a medical institution.  
         [0037]     In the medical institution, when conducting surgical treatment of an affected part using the holding forceps  1  while observing the affected part by the endoscope, the holding forceps  1  is taken out from the sterilized bag for use in a predetermined treatment. After having completed the treatment, in order to sterilize the holding forceps  1  in a sterilizing apparatus for ethylene oxide gas sterilization (EOG sterilization), autoclave sterilization, or hydrogen peroxide low-temperature plasma sterilization, which are popular sterilizing methods, the holding forceps  1  is stored in a sterilizing chamber and the sterilizing chamber is evacuated to produce a vacuum. At this time, the atmospheric pressure around the holding forceps  1  becomes negative with respect to the air pressure in the air chamber  10  in the recess  7 , and hence a difference in air pressure results between the inside and the outside of the air chamber  10 . When the difference in air pressure exceeds a predetermined value, the partitioning wall member  9  adhered and fixed to the peripheral edge portion  8  of the recess  7  is separated as shown in  FIG. 3 , and the do-not-reuse indication displayed on the bottom surface of the recess  7  is exposed and visible. Since the do-not-reuse indication is exposed when the partitioning wall member  9  is separated, the operator can verify the fact that the holding forceps  1 , with the partitioning wall member  9  separated, is an SUD medial device and that the sterilizing process for reuse has been conducted for the holding forceps  1  (which is a SUD medical device in which sterilization is prohibited). Therefore, the operator can easily judge whether the holding forceps  1  is reusable or not.  
         [0038]     The recess  7  covered by the partitioning wall member  9  and used for the do-no-reuse indication may be any shape and size which enables visual recognition of the do-not-reuse indication. Furthermore, the recess  7  can be provided at any position on the operating unit  3 . Therefore, a versatile do-not-reuse indication can be employed in many types of SUD medical devices.  
         [0039]     Although the holding forceps  1  are described above as an example, the invention can be also applied to various treatment forceps such as an incision forceps, e.g. an electric surgical knife or a high-frequency knife for incising viscous membranes other than the holding forceps.  
         [0040]     As another application of the first embodiment, as shown in  FIG. 5 , a tag  11  to be attached to the SUD medical device can be employed. The tag  11  includes a connecting member  12  to be connected and fixed to the SUD medical device, and a recess (not shown) covered by a partitioning wall member  13  provided on one side of the tag  11 . The recess covered by the partitioning wall member  13  of the tag  11  has the same structure as the recess  7  described above, and the partitioning wall member  13  is the same as the partitioning wall member  9  described above.  
         [0041]     Since the tag  11  can be attached easily to various SUD medial devices, when the atmospheric pressure in the chamber becomes negative when being stored in the chamber and conducting the sterilizing process, the partitioning wall member  13  of the tag  11  is separated and hence the do-not-reuse display provided on the recess is exposed and visible, whereby recognition of the fact that the device is a sterilized SUD medical device and verification of being sterilized are enabled.  
         [0042]     Subsequently, referring to  FIG. 6  to  FIG. 8 , the medical device according to a second embodiment will be described. The same parts as the medical device described based on  FIG. 1  and  FIG. 2  are represented by the same reference numerals and detailed description thereof is omitted.  
         [0043]     The holding portion  6 , which is held by the operator, of the operating unit of the holding forceps  1  as the SUD medical device according to the second embodiment is formed with a notch  14  cut into a V-shape opening from a proximal side toward a distal side, which is opposite from the handle  5 , as shown in  FIG. 6 . The notch  14  has a depth such that when the operator holds the holding portion  6  and operates the handle  5  toward the holding portion  6 , the holding portion  6  is broken by the operating force from the notch  14  as shown in  FIG. 8 .  
         [0044]     A cover member  15  is adhered and fixed to the peripheral edge of the opening of the notch  14  so as to cover the notch  14 . The cover member  15  is a reinforcing member adhered and fixed to the peripheral edge of the opening of the notch  14  for preventing the holding portion  6  from being broken by a force exerted to the holding portion  6  when the handle  5  is operated. An air chamber  10  is defined by the notch  14  and the cover member  15 .  
         [0045]     Adhesion and fixation of the cover member  15  to the peripheral edge of the opening of the notch  14  is performed under the ambient pressure as in the case of the first embodiment described above. The cover member  15  is adhered and fixed to reinforce the holding portion  6  so as not to be broken from the notch  14  and to prevent leakage of air from the air chamber  10  toward the outside. The cover member  15  is adhered and fixed so as to be separated easily when the outside air pressure becomes negative, thus exceeding a predetermined magnitude with respect to a difference between the pressure in the air chamber  10  and the outside pressure.  
         [0046]     When the holding forceps  1  is stored in a chamber for sterilization for performing, for example, EOG sterilization and bringing the inside of the chamber into a negative pressure after having used the holding forceps  1  as the SUD medical device in this configuration under the endoscopic observation by the operator, a difference in pressure between the internal air pressure in the air chamber  10  and the external atmospheric pressure is resulted, and the cover member  15  is separated from the peripheral edge of the opening of the notch  14  when such pressure difference exceeds a predetermined value.  
         [0047]     In the holding forceps  1  with the cover member  15  separated from the notch  14 , when the handle  5  of the operating unit  3  is operated, the operating force generates a moment which bends the bottom of the holding portion  6  toward the handle  5  from the notch  14  of the holding portion  6 . Consequently, as shown in  FIG. 8 , the holding portion  6  is broken. According to the second embodiment, since the holding portion  6  is broken, the holding forceps  1  cannot be reused, and hence reuse of the SUD medial device is prevented in advance of a reuse.  
         [0048]     Referring now to  FIG. 9  to  FIG. 13 , a medical device according to a third embodiment will be described.  
         [0049]     A function restricting module  16  used in a SUD device as a medical device according to a third embodiment restricts reuse of the SUD medical device by restricting or disabling at least part of the function of the medical device. The function restricting module  16  includes a slider member  17  and a cylindrical member  18  as shown in  FIG. 9 . The slider member  17  includes a piston portion  19 , a shaft portion  21 , a pin portion  23  and a male engaging portion  24 . The piston portion  19  is provided at a first end of the slider member  17 , and formed into a disk shape. The shaft portion  21  extends by a predetermined dimension from the axial center of the piston portion  19  to another end, and has a column shape having an outer diameter smaller than the piston portion  19 . The pin portion  23  extends axially by a predetermined dimension towards the other end of the shaft portion  21 , and has a column shape having an outer diameter smaller than the shaft portion  21 . The male engaging portion  24  is provided on the outer periphery at a boundary position between the pin portion  23  and the shaft portion  21 .  
         [0050]     The cylindrical member  18  includes a cylinder portion  20 , a supporting portion  22 , and a female engaging portion  26 . An outer periphery of the piston portion  19  of the slider member  17  is fitted into the cylinder portion  20 , and the piston portion  19  slides therein. The supporting portion  22  is formed on the central portion of the inner periphery of the cylinder portion  20  and the outer periphery of the shaft portion  21  of the slider member is fitted into the supporting portion  22  and slides therein. The female engaging portion  26  is provided in the radial direction at the other end of the cylinder portion  20  with respect to the supporting portion  22 , and the pin portion  23  of the slider member  17  is fitted and slides therein, and is provided on the outer periphery around a boundary between the pin portion  23  and the shaft portion  21 .  
         [0051]     In other words, when a distal end of the pin portion  23  of the slider member  17  is inserted through the cylinder portion  20 , the supporting portion  22  and the female engaging portion  26 , the piston portion  19  is slidably fitted to the internal periphery of the cylinder portion  20 , the shaft portion  21  is slidably fitted to the supporting portion  22 , and the pin portion  23  is slidably fitted to the female engaging portion  26  respectively.  
         [0052]     The piston portion  19  of the slider member  17  is slidably fitted into the cylinder portion  20  of the cylindrical member  18 , and a space defined between the piston portion  19  and the supporting portion  22  is an air chamber  28 . In order to communicate the air chamber  28  defined by the piston portion  19  and the supporting portion  22  with the outside air, an air ventilation hole  25  is formed through a portion near the supporting portion  22 .  
         [0053]     As shown in  FIG. 9 , in the function restricting module  16  in this arrangement, the piston portion  19  of the slider member  17  is fitted to the inner periphery of the cylinder portion  20 , the shaft portion  21  of the slider member  17  is fitted to the supporting portion  22  of the cylindrical member  18 , the pin portion  23  of the slider member  17  is fitted to the female engaging portion  26  of the cylindrical member  18 , whereby the air chamber  28  is defined by the piston portion  19 , the cylinder portion  20  and the supporting portion  22 . In a state in which the male engaging portion  24  provided on the shaft portion  21  is positioned between the supporting portion  22  and the female engaging portion  26 . It is assumed that the SUD medical device having the function restricting module of this embodiment is stored in the sterilizing chamber for sterilization and the atmospheric pressure of the cylindrical member  18  becomes negative. Then, the atmosphere of the air chamber  28  is evacuated (the pressure inside of the sterilization chamber decreases) through the air-ventilation hole  25 . Therefore, as shown in  FIG. 10 , the piston portion  19 , the shaft portion  21 , and the pin portion  23  slide distally (i.e., toward the left in  FIG. 10 ). Consequently, the male engaging portion  24  of the shaft portion  21  engages and locks with the female engaging portion  26  on the cylindrical member  18 . In other words, the slider member  17  slidably inserted into the cylindrical member  18  is slid by the atmospheric pressure and hence the male engaging portion  24  provided on the shaft portion  21  engages with the female engaging portion  26 , whereby the pin portion  23  of the slider member  17  is axially projected from the cylindrical member  18  and locked at a predetermined position. By the engagement and locking between the male engaging portion  24  and the female engaging portion  26 , the slider member  17  cannot be restored to its original position even when the atmospheric pressure changes.  
         [0054]     The function restricting module  16  is stored and disposed in a holding portion  29  of a holding forceps  27 , which is the same as the holding forceps  1  as described above in the first and second embodiments as shown in  FIG. 11  so that the pin portion  23  projects toward the handle  28  side. In other words, at the time of manufacture of the holding forceps  27  as the SUD medical device, the function restricting module  16  in a state shown in  FIG. 9  is disposed in the holding portion  29  of the holding forceps  27 . When the handle  28  of the holding forceps  27  provided with the function restricting module  16  in this state is operated, the holding portion provided at the distal end of the insertion portion, not shown, of the holding forceps  27  can be opened and closed.  
         [0055]     When the operator performs the treatment using the holding forceps  27  provided with the function restricting module  16 , and the holding forceps  27  are stored in the sterilizing chamber, for example, for EOG sterilization to brings the inside of the chamber into a negative pressure, a differential pressure is resulted between the internal air pressure in the air chamber  28  of the function restricting module  16  stored and disposed in the holding portion  29  and the atmospheric pressure on the outside, and the slider member  17  slides to the position shown in  FIG. 10 . Then, the pin portion  23  projects toward the handle  28 , and the male engaging portion  24  and the female engaging portion  26  are engaged and locked. Accordingly, if the operator operates the handle  28  of the holding forceps  27  after the EOG sterilization, the handle  28  abuts against the pin portion  23  and hence the operation of the handle  28  is disabled and reuse for another treatment is prevented. The cylinder portion or function thereof can also be integrally formed with the holding portion  29  or other portion of the holding forceps  27 .  
         [0056]     Subsequently, an example in which the function restricting module  16  is used in a trocar  30  as shown in  FIG. 12  will be described. The function restricting module  16  is stored and disposed in the cylindrical member  31  in which an inner needle (not shown) of the trocar  30  is inserted in the orthogonal direction. In other words, at the time of manufacturing the trocar  30 , which is the SUD medical device, the function restricting module  16  is stored and disposed in a state in which a distal end of the pin portion  23  is directed to the cylindrical member  31  of the trocar  30  as shown in  FIG. 9 . The inner needle is inserted to the trocar  30  provided with the function restricting module  16  in this state from the cylindrical member  31 , and then the treatment is performed.  
         [0057]     After having finished the treatment using the trocar  30  provided with the function restricting module  16  by the operator, if the trocar  30  is stored in the chamber for EOG sterilization and the inside of the chamber is brought into a negative pressure, a difference results between the internal air pressure in the air chamber  28  of the function preventing module  16  stored and disposed in the trocar  30  and the atmospheric pressure on the outside, and the slider portion  17  slides to the position shown in  FIG. 10 . Then, the pin portion  23  projects into the cylindrical member  31 , and the male engaging portion  24  and the female engaging portion  26  are engaged and locked. Accordingly, if the operator inserts the inner needle or other instrument into the cylindrical member  31  of the trocar  30  after the trocar  30  is subjected to EOG sterilization, the inner needle abuts the pin portion  23 , and hence insertion of the inner needle is disabled, whereby reuse for another treatment is prevented.  
         [0058]     In addition, a case in which the function restricting module  16  is used in displacement forceps  32  as shown in  FIG. 13  will be described. The operating unit  34  at the proximal end on the operator&#39;s side is provided with a dial  33  for opening and closing the distal end of forceps (not shown) for holding an internal organ in the body cavity. In other words, it is adapted to be capable of adjusting the opening and closing angle of the distal end of the forceps when rotating the dial  33 . A hole  35  is provided on part of the dial  33  of the operating unit  34  of the displacement forceps  32 . In a state in which the distal end of the forceps is brought into a closed state by rotating the dial  33 , the function restricting module  16  in a state shown in  FIG. 9  is stored in the operating unit  34  so that the pin portion  23  of the function restricting module  16  is positioned immediately below the hole  35  provided on the dial  33 .  
         [0059]     If the operator stores the displacement forceps  32  provided with the function restricting module  16  in the sterilizing chamber for performing for example, EOG sterilization after having completed the treatment using the displacement forceps  32 , and the chamber pressure becomes negative, a difference between the internal air pressure in the air chamber  28  of the function restricting module  16  stored and disposed in the operating unit  34  of the displacement forceps  32  and the external atmospheric pressure results, and the slider portion  17  slides to the position shown in  FIG. 10 . Then, the pin portion  23  projects into the hole  35  provided on the dial  33 , and the male engaging portion  24  and the female engaging portion  26  are engaged and locked. Accordingly, the pin portion  23  projects from the hole  35  on the dial  33  of the displacement forceps  32  after the EOG sterilization  32 , the dial  33  can no longer be rotated, whereby reuse for another treatment is prevented.  
         [0060]     In this manner, by storing and arranging the function restricting module  16  at a position where the operation of the main function of the SUD medical device can be restricted, the SUD medical device can be brought into a state in which reuse is restricted. Therefore, the function restricting module  16  can be applied to a plurality of types of SUD medical devices and is superior in versatility.  
         [0061]     While there has been shown and described what are considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention not be limited to the exact forms described and illustrated, but constructed to cover all modifications that may fall within the scope of the appended claims.