Abstract:
A disposable apparatus for use in blood testing and being adapted for simultaneous dilution of a blood sample into two different dilution ratios, said apparatus including a block-shaped housing having integrated therein a first and a second receptacle, one of which as a first blood sample receiver being adapted to receive a blood sample; a first and a second container, each containing a defined volume of a diluting agent; a valve including a valve body having three valve body channels extending therethrough and being positionable in three distinct positions, one of which putting the receptacles in simultaneous communication with a respective one of the containers through pairs of the channels; and displacers for displacing the diluting agent and the diluted sample through said channels between said containers and said receptacles.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a Continuation of Application Ser. No. 10/849,239, filed May 20, 2004, now U.S. Pat. No. 7,335,339 and claims priority under 35 U.S.C. §119 to Swedish Patent Application No. 2001-0103877-7, filed Nov. 21, 2001, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a disposable apparatus for use in blood testing. 
     2. Description of Background Art 
     When making blood tests in the field, it is a desire to perform such tests with simple but reliable apparatus that can be handled even by relatively untrained personnel. Still, there exists the requirement that a blood sample shall be taken and handled under strict hygienic conditions, and that neither the sample itself or residues thereof, nor diluting or flushing liquids used when testing the sample shall risk to be contacted by humans. Thus, there shall be no waste matter and all contaminated material shall remain within the apparatus. 
     It is known in the state of art to count blood cells by causing a volume of diluted blood sample to pass a so-called capillary, i.e., an extremely small hole, generally in a ruby, the hole having a diameter considerably larger than the size of a blood cell, typically 80 μm. A voltage is applied over the capillary, and, when a blood cell passes through the hole, the electrical resistance changes. This is because the cells can be regarded as insulators. Each change in resistance can be detected by suitable electronic equipment, and the sum of all changes detected corresponds to the number of blood cells having passed through the capillary. In order to obtain the concentration of cells in the original sample, the concentration of cells in the diluted sample is multiplied by the dilution factor, typically 1:40000 when counting of red blood cells (RBC) is concerned. It is obvious, that measuring of sample volumes and dilution liquid volumes must be performed in an accurate and repeatable way such that not only a correct degree of dilution can always be guaranteed but also a thorough and uniform mixing of the two volumes is ensured. 
     A disposable sampling device for an apparatus for counting particles contained in a liquid, such as blood cells in a blood sample, is known from WO 99/01742. This device is capable of making one diluting step. 
     A blood testing apparatus for performing dilution of a small defined volume of blood sample contained in a capillary tube is described in U.S. Pat. No. 6,284,548. The dilution involves a pre-dilution step and a final dilution step. 
     A device for diluting and mixing a liquid sample, such as a blood sample for performing a CRP test, is described in WO 01/75416. The sample is contained in a capillary tube and is mixed in a first step with a diluting agent to provide a diluted sample. In a second step, a third medium, such as antibodies, may be mixed with the diluted sample. 
     Even if some of the prior art devices are capable of making two dilutions, none of them is capable of making two simultaneous dilutions to different dilution ratios, which is desirable in order to perform, e.g., simultaneous counting of white and red blood cells. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     It is a main object of the present invention, thus, to provide a disposable apparatus for use in blood testing, which allows simultaneous dilution of a blood sample to two defined dilutions ratios. Also, in order to avoid waste, the disposable apparatus shall be capable of retaining all contaminated material within itself. It is also an object of the present invention to propose an instrument for use with the apparatus. 
     To fulfill the main object above, the present invention proposes a disposable apparatus for use in blood testing and being adapted for simultaneous dilution of a blood sample into two different dilution ratios, said apparatus including a block-shaped housing having integrated therein: a first and a second receptacle, one of which, as a first blood sample receiver, being adapted to receive a blood sample; a first and a second container, each containing a defined volume of a diluting agent; a valve including a valve body having three valve body channels extending therethrough and being positionable in three distinct positions, one of which bringing the receptacles in simultaneous communication with a respective one of the containers through pairs of the channels; and displacers for displacing the diluting agent and the diluted sample through said channels between said containers and said receptacles. The displacers may be pistons movable in cylinders provided in the housing, or, an external source of pressure may be utilized to displace the diluting agent and the diluted sample. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in connection with an embodiment thereof utilizing a turning valve, and pistons as displacers, reference being made to the accompanying schematic drawings, wherein: 
         FIG. 1  is a front view showing the apparatus in its preparatory state including a capillary tube held by a cover; 
         FIG. 2  is a corresponding view showing the apparatus with its capillary tube and cover removed; 
         FIG. 3  is a view showing the removed capillary tube in a position receiving a blood sample from punctured finger tip; 
         FIG. 4  is a view corresponding that of  FIG. 2  showing the apparatus with the capillary tube and its blood sample relocated in its original position within the apparatus; 
         FIG. 5  is a front view of the apparatus as shown in  FIG. 4  having the turning valve rotated one step to a second position; 
         FIGS. 6   a  and  b  are front views showing the apparatus in its preparatory state according to  FIG. 1  and illustrating a further possibility to charge the apparatus with a blood sample; 
         FIG. 7  is a view corresponding to that of  FIG. 6   b  showing the apparatus with the turning valve rotated one step to a second position; 
         FIG. 8  is a front view of the apparatus as shown in  FIGS. 5 and 7  connected to schematically shown external fluid conduits and valve and plunge actuating means of a test instrument; 
         FIG. 9  is a side view of the apparatus as shown in  FIG. 8  and parts of the test instrument; 
         FIG. 10  is a front view of the apparatus shown in the valve position of  FIGS. 5 ,  7  and  8  and with its plungers displaced to their extreme positive position; 
         FIG. 11  is a front view of the apparatus having its plungers in an intermediate position and its valve rotated a further step to a third position; 
         FIG. 12  is a front view of the apparatus having its valve in the third position and its plungers displaced to their extreme positive position; 
         FIG. 13  is a view corresponding to that of  FIG. 8 , but showing the valve in its third position and its plungers moving towards their extreme positive positions; and 
         FIG. 14  is a view corresponding to that of  FIG. 13 , but showing the plungers in their extreme negative position after having performed a flush stroke. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is evident for the skilled person that the present invention may as well be practiced utilizing a sliding valve instead of the turning valve specifically described. I the following description, the terms upper, lower, right, left etc., refer to the position of the apparatus shown in the various Figures. 
     The overall structure of the apparatus will first be described with reference to  FIG. 1 . It consists of a block-like housing  1  (see also the side view of  FIG. 9 ) preferably made of a translucent, moldable material. The housing has an upper end  2 , a bottom end  3 , a left side wall  4 , a right side wall  5 , a front wall  6  and a rear wall  7  seen in  FIG. 9  only. 
     In a central portion of the housing is provided a cylindrical hole  8 . Two channels  9  and  10  extending towards the upper end  2  open in the hole  8  at spaced locations along its upper circumference. Correspondingly, two channels  11  and  12  extending towards the bottom end  3  open in the hole  8  at spaced locations along its lower circumference. 
     A turning valve body  13  dimensioned to fit into the hole  8  is placed therein so as to be rotatable between at least three distinct positions. Three separate channels, a first channel  14 , a second channel  15  and a third channel  16 , extend through the valve body between mutually diametrically opposed positions along the circumference of the valve body. The channels are angularly spaced such that there is a substantially 60° angular distance between them along the circumference. By turning the valve body, the channels  14 - 16  may be positioned so as to cross-wise put the channels  9 / 12  and  10 / 11  in communication with one another. 
     The valve body is shown in  FIG. 1  in a first rotational position I. In this position, the preparatory position, none of the channels  14 - 16  communicate with the channels  9 / 12  and  10 / 11 . It can be seen however, that one end of the channel  14  communicates with a channel  17  extending between a position along the left portion of the circumference of the hole  8  and the left side wall  4 , and that its opposite end communicates with a channel  18  extending between an opposed portion along the right portion of the circumference of the hole  8 . The purpose of this communication will be explained later with reference to  FIGS. 6 and 7 . 
     In the upper portion of the housing  1  are formed two receptacles  19 ,  20 , preferably formed like parallel bores. A first one of these, receptacle  19 , has its lower end  19 ′ connected to the channel  9 . Its upper end is shown to be closed, but it may as well be open and closed by any suitable removable cover. A second one of the receptacles, receptacle  20 , has its lower end  20 ′ connected to the channel  10 . Its upper end is closed by a preferably circular cover  21  snapped into engagement with a hook-like protrusion  22  formed at the upper end  2  of the housing. 
     The cover  21  is shown to carry a capillary tube  23  having an upper end  24  and a lower end  25 . The tube is mounted in the cover by means of ribs  26  depending from the cover such that the upper end of the tube opens in an open space between the ribs communication with atmosphere. 
     As an alternative option, there may be provided a separate cover  21  to close the receptacle  20  and a separate combination of a cover  21  and a capillary tube as shown. 
     In the lower portion of the housing  1  are formed two parallel cylinders  27 ,  28 . A first one of these, cylinder  27 , has its upper end  27 ′ connected to the channel  11 . A second of the cylinders  28  has its upper end  28 ′ connected to the channel  12 . A first piston  29  is slidably reciprocatingly movable along the cylinder  27 . A second piston  30  is slidably reciprocatingly movable along the cylinder  28 . The pistons have piston rods  29 ′,  30 ′, respectively, each having in a lower end thereof a through hole  29 ″,  30 ″, respectively. The holes  29 ″,  30 ″ are accessible through vertically extending apertures  7 ′ in the rear wall  7  of the housing. 
     The right hand wall  5  of the housing is provided with a cylindrical protrusion  31 , in the centre of which opens the channel  18  with a slightly widening mouth portion  18 ′. An elastic diaphragm  32  seals the mouth portion  18 ′. In the preparatory state of the apparatus, the cylinders  27  and  28  are both filled with well-defined volumes, typically 2 ml, of diluting agent D 1 , D 2 , respectively, typically isotonic sodium chloride solution. Furthermore, the channel  16  is filled with an appropriate amount of a haemolysis agent H, which may be in a dried or a fluid state. In the first position I of the valve body  13 , where the ends of the channel  16  are located at a distance from any one of the housing channels  9 ,  12 ,  17 ,  18 , the haemolysis agent H is effectively prevented from escaping the channel  16 . 
     In a first mode of operation shown in  FIGS. 2 and 3 , the apparatus is used in finger tip blood sampling. The cover  21 —and with it the capillary tube  23 —is removed from the housing  1 , and a blood sample S is taken with the capillary tube as illustrated in  FIG. 3 . The tube is approached to a drop of blood B formed on a punctured finger tip F, and the drop is sucked up by capillary action to completely fill the tube with a defined volume of sample S. During this operation, the cover  21  serves as a handle, thus avoiding any contact with the sample. After the sample is taken, the capillary tube is re-inserted into the receptacle  20  as seen in  FIG. 4 , and the cover  21  is pushed down to snap into sealing contact with the protrusions  22 . In this position, the lower end  25  of the capillary tube may be more (as shown) or less introduced into the channel  10 . 
     In the state according to  FIG. 4 , the turning valve  13  is rotated one step counterclockwise to the second rotational position II shown in  FIG. 5 , where the housing channels  9  and  12  communicate through valve channel  15  and the housing channels  10  and  11  communicate through valve channel  14 . In practice, the housing is placed in an associated instrument, as will be described later, for automatic performance of the valve rotation. 
     In a second mode of operation shown in  FIGS. 6   a  and  6   b , the apparatus is used in venipuncture sampling. When taking a venipuncture sample, blood is introduced into the channel  18  to pass into and through the valve body channel  14 . This is suitable made by an injection needle or cannula  33  by which the diaphragm is pierced. Preferably, a so-called vacuutainer sleeve  34  is used, i.e., a device commonly used in connection with a so-called vacuutainer. A vacuutainer sleeve is a cylindrical hollow body having a bottom  34 ′ centrally carrying the needle  33 , and having an open end  34 ″. The needle has both its end chamfered so as to provide sharpened points  33   a ,  33   b . The exterior dimension of the protrusion  31  is adapted to the interior dimension of the open end  34 ″ of the vacuutainer sleeve, so that the latter may be pushed onto the protrusion  31  with the needle point  33   a  penetrating the diaphragm  32  and being introduced into the channel mouth  18 ′. In this position, the housing  1  with the vacuutainer sleeve may be manipulated so as to bring the needle point  33   b  to puncture a vein. The venous pressure will force blood through the needle  33 , the channel  18 , the channel  14  into the channel  17  as seen in  FIG. 6   b , where a sample S is shown to occupy the interiors of the needle  33  and the channels  18 ,  14  and  17 . A widened portion  17 ′ of the channel  17  is suitably provided with a plug  35  of a material, such as a textile material, having the properties to allow air, but preventing blood flow therethrough. After the sample is taken, the needle point  33   b  is withdrawn from the punctured vein and, subsequently, the needle point  33   a  is withdrawn from the channel mouth  18 ′ and from the pierced diaphragm  32 . Due to the elasticity of the latter, it will seal itself and prevent any escape of blood from the portion of the sample within the channel  18 . 
     In the state according to  FIG. 6   b , the turning valve  13  is rotated one step counterclockwise to the second rotational position II shown in  FIG. 7 , thereby separating the defined volume of blood sample S contained within the channel  14  from the volumes contained within the housing channels  17  and  18 , and further placing the housing channels  9  and  12  in mutual communication through the valve body channel  15  and the housing channels  10  and  11  in mutual communication through the valve body channel  14 . In practice, the housing is placed in an associated instrument, as will be described later, for automatic performance of the valve rotation. 
     It is noted in  FIG. 7 , that the capillary tube  23  is shown in dotted lines to indicate its option in this mode, whereas the cover  21  is shown in full lines. It is furthermore noted, that the rotational positions II of the valve body  13  shown in  FIGS. 5 and 7  are the very same, and that the only difference is that the blood sample S is within the capillary tube  23  in  FIG. 5  and within the valve body channel  14  in  FIG. 7 . In this position, common to both modes of operation, both pistons  29  and  30  are operated in a positive (i.e., upward) direction so as to displace the defined volume of diluting agent D 1  from the cylinder  27  through the channels  11 ,  14  and  10  into the receptacle  20 , and so as to displace the defined volume of diluting agent D 2  from the cylinder  28  through the channels  12 ,  15  and  9  into the receptacle  19 . 
     Turning now to  FIGS. 8 and 9 , these figures show the apparatus housing  1  placed in an instrument having means for rotating the turning valve body  13  and for operating the pistons  29 ,  30 , as well as means for performing certain measurements. 
     As shown in  FIG. 8 , the valve body  13  is provided with two diametrically opposed holes  36 ,  37 . When the apparatus housing is placed in the instrument, two operating arms  38 ,  39  of a rotatable valve operating member  40  engage in a respective one of these holes as seen in the side view of  FIG. 9 . Simultaneously, two piston operating arms  41   a ,  41   b  engage in a respective one of the through holes  29 ″,  30 ″ in the piston rods  29 ′,  30 ′. The valve operating member  40  is rotatable in the directions of the double arrow R in  FIG. 8 , and the piston operating arms  40 ,  41  are vertically movable so as to move the pistons in the directions of the double arrow P in  FIG. 9 . Such movement is preferably simultaneous for both pistons. 
       FIG. 8  shows a situation corresponding to that of  FIG. 5 , i.e., with the blood sample S within the capillary tube  23 . An upward stroke of the piston  29  will direct the diluting agent D 1  through the channel  10  (see  FIG. 10 ) and at least partly through the capillary tube  23  having its lower end  25  introduced therein. Consequently, the sample S will be displaced upwardly from the capillary tube and flow from its upper end  24  down into the receptacle  20 , where it will mix with parts of the diluting agent having passed through the annular space  10 ′ formed between the lower end  25  of the capillary tube and the channel  10 . A subsequent downward stroke of the piston  29  will withdraw the mixture (S+D 1 ) of sample S and diluting agent D 1  from the receptacle  20  through the annular space  10 ′ to flow into the cylinder  27 . Further subsequent strokes according to the arrow P will complete this mixing operation, which is a first stage mixing operation. Simultaneous strokes of the piston  30  in the directions P will only force the diluting agent D 2  from the cylinder  28  into the receptacle  19  and back. 
     In the second mode of operation, an upward stroke of piston  29  will displace the diluting agent D 1  through the channel  14  and consequently bring along the defined volume of sample S contained within the channel  14  directly into the recipient  20  in case there is no capillary tube  23  present, and partly through such tube if one is present. Subsequent strokes according to arrow P will complete the first stage mixing operation as in the first mode of operation. 
     In  FIG. 8  is shown a circle indicating a light path  42  through the cylinder  27 . This light path is also shown in  FIG. 9  to extend between a light source  43  and a detector  44 . The light path may be used to measure firstly a reference value of the diluting agent D 1  and subsequently a value after the first stage diluting step, i.e., of the diluted sample (S+D 1 ). 
       FIG. 10  shows the situation during the first mixing operation when the pistons are reciprocating in the directions of arrows P to complete the mixing. The pistons are halted in an intermediate position shown in  FIG. 11  leaving a major portion of the diluted sample (S+D 1 ) in the cylinder  27 , and above all, a defined volume of first stage diluted sample in the channel  14 . 
     In a following step, the turning valve is rotated counterclockwise to its third position III, where its channel  14  connects channels  9  and  12 , and its channel  16  connects the channels  10  and  11  ( FIG. 11 ). In this rotational position, channel  14  contains a defined volume of sample S and diluting agent D 1  (S+D 1 ), whereas channel  16  still contains its original contents of haemolysis agent H. 
     Upward movement of the piston  29  as shown in  FIG. 12 , displaces the diluted sample (S+D 1 ) through the valve channel  16  to convey the haemolysis agent H therefrom into the recipient  20  to mix with the first stage mixture (S+D 1 ) to form a mixture (S+D 1 +H). Simultaneous upward movement of piston  30  displaces the diluting agent D 2  from the cylinder  28  through the valve channel  14  containing a defined volume of first stage diluted sample S+D 1 . This first stage sample, thus, will be mixed with the volume of diluting agent D 2  present in recipient  19  to provide a second stage diluted sample (S+D 1 +D 2 ). Subsequent reciprocating movement of the pistons will complete the two simultaneous mixing processes, leaving a final dilution ratio of typically 1:200 in the cylinder  27  and the receptacle  20 , and a final dilution ratio of typically 1:40000 in the cylinder  28  and the receptacle  19 . 
     After this final dilution step, the measurements on the two differently diluted samples (S+D 1 +H) and (S+D 1 +D 2 ) are performed with the instrument mentioned. Apart from its operating arms, the instrument includes a measuring system having means for conducting at least parts of the contents in the receptacles  19  and  20  past measurement stations, where particle counting is performed, as well as means for controlling the volumes to be measured and means for flushing the various conduits of the measuring system. Such means are shown in  FIGS. 8 ,  9 ,  13  and  14 . 
     The measuring system includes two similar conduit branches  45   a ,  45   b , one for each of the receptacles  19 ,  20 . Each such branch starts with a needle portion  46   a ,  46   b  directed in parallel with the arms  38 - 41  so as to pierce corresponding diaphragms  47   a ,  47   b  sealing apertures  48   a ,  48   b  in the rear housing wall  7  communicating with the receptacles  19 ,  20 , respectively. 
     The needle portions are in fluid communication with conduits  49   a ,  49   b . These are provided with cell counting stations  50   a ,  50   b , each comprising a first electrode  51   a ,  51   b , an orifice  52   a ,  52   b  and a second electrode  53   a ,  53   b . The orifices are small apertures allowing statistically only one blood cell to pass at a time. By means of electric wires  54   a ,  55   a  and  54   b ,  55   b , respectively, a voltage may be applied over the orifices, and any change in the resistance between the electrodes, indicating the passage of a blood cell to be counted, may be detected by suitable electronic equipment included in the instrument, and the sum of all resistance changes detected corresponds to the number of blood cells having passed through the orifice. 
     Each of the conduits  49   a ,  49   b  is branched into two sub-branch conduits  56   a ,  56   b  and  57   a ,  57   b , respectively. The conduits  56   a ,  56   b  lead to a respective container  58   a ,  58   b  containing a flush liquid F. The flush liquid also fills the conduits  56   a ,  56   b  as well as the conduits  49   a ,  49   b  including the needle portions  47   a ,  47   b . Valves  59   a ,  59   b  are mounted in the conduits  56   a ,  56   b  between the containers  58   a ,  58   b  and the sub-branch conduits  57   a ,  57   b , respectively. Valves  60   a ,  60   b  are also mounted in the conduits  57   a ,  57   b . The flush liquid F is filled into the conduits  56   a ,  56   b  to a level LF above the valves  60   a ,  60   b.    
     Substantially vertical portions of the conduits  57   a ,  57   b  are provided with lower counting start detectors  61   a ,  61   b  and upper counting stop detectors  62   a ,  62   b  spaced defined distances. 
     After completing the simultaneous mixing operations described above with reference to  FIG. 12 , and before commencing the particle counting process, the valves  59   a ,  59   b  are closed, whereas the valves  60   a ,  60   b  are opened. Furthermore, the pistons  29 ,  30  must be brought to positions where the levels in the receptacles  19  and  20  are located above the needle portions  46   a ,  46   b , as seen in  FIG. 13 . 
     From these positions, the pistons are further displaced upwards to press the respective contents of the receptacles  19 ,  20  through the needle portions  46   a ,  46   b  and into the conduits  49   a ,  49   b . During this process, the flush liquid contained within the needle portions and the conduits will be displaced through the conduits  49   a ,  49   b , including the electrodes  51   a ,  51   b , the orifices  52   a ,  52   b  and the electrodes  53   a ,  53   b , through the open valves  60   a ,  60   b  to raise the original level LF towards the respective lower detector  61   a ,  61   b.    
     It should be emphasised at this stage of the description, that the various conduits shown in the drawings are not drawn in proper relative scales. In practice, and as will be evident for the skilled person, the volumes within the conduits  49   a ,  49   b , including the needle portions  47   a ,  47   b , up to the second electrodes  53   a ,  53   b , are at least equal to the volumes within the conduits  57   a ,  57   b  between the valves  60   a ,  60   b  and the counting start detectors  61   a ,  61   b.    
     In other words, the dimensioning of the conduits is such, that when the levels of the flush liquid in the vertical conduits  57   a ,  57   b  have reached the counting start detectors  61   a ,  61   b , the respective diluted sample shall at least have reached its associated second electrode  53   a ,  53   b , respectively. 
     Thus, when the level of the flush liquid has reached the respective counting start detector  61   a ,  61   b , a signal is delivered to the instrument to start particle counting, i.e., to start recording each resistance change detected over the electrodes  51   a ,  53   a  and  51   b ,  53   b , respectively. As soon as the levels LF in the conduits  57   a ,  57   b  have reached the respective upper detector  62   a ,  62   b , a stop counting signal is delivered to the instrument, and the corresponding results may be stored in the instrument and/or displayed on it. 
     During the counting process, the diluted blood samples never reach further along the conduits than to positions well before the respective branching point  49 ′ of the conduits  49   a ,  49   b.    
     After the counting process has been completed, the pistons  29 ,  30  are returned to positions where the levels LF in the conduits  57   a ,  57   b  are substantially as before starting the counting. 
     At this stage, the valves  60   a ,  60   b  are closed, the valves  59   a ,  59   b  are opened, and the pistons  29 ,  30  are lowered to their bottom positions as shown in  FIG. 14 . During this process, flushing liquid F is withdrawn from the respective container  58   a ,  58   b  through the conduits  56   a ,  56   b  to completely flush through the conduits  49   a ,  49   b,  including the second electrodes  53   a ,  53   b , the orifices  52   a ,  52   b , the first electrodes  51   a ,  51   b , and the needle portions  46   a ,  46   b.    
     In this position, all possibly contaminated liquid is contained within the cylinders  27 ,  28 . When finally removing the disposable apparatus housing  1  from the instrument, the elastic diaphragms  47   a ,  47   b  will effectively wipe off any diluted sample residue from the needle portions  46   a ,  46   b.    
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.