Abstract:
System apparatus for determining the volume of a potable liquid ingested by a small laboratory animal over an extended period of time is provided with a liquid dispensing section that has a liquid delivery tube and sipping tube combination, that retains a drop/droplet of the potable liquid in a position accessible to the animal, and that replaces each drop/droplet of liquid ingested by the animal with a succeeding drop/droplet of liquid, counting the total number of drops/droplets ingested by the animal over an extended period of time.

Description:
CROSS-REFERENCES 
     None. 
     FIELD OF THE INVENTION 
     This invention relates generally to monitoring of liquid intakes by a small animal, and particularly concerns both apparatus and methods that are usefull in connection with research operations requiring the detection and precision measurement of a liquid ingested by a small laboratory animal over an extended period of time. 
     BACKGROUND OF THE INVENTION 
     There are two well-known classical methods for measuring the volume of liquid ingested by a laboratory animal. The first such method counts animal licks of the liquid-dispensing device. Each time an animal lick of the sipping tube occurs a tube lick counter is activated, and subsequently the total lick count is used in arithmetically determining the total amount of liquid ingested by the animal over the period of time involved by multiplying the lick count by a presumed unit liquid volume intake per animal lick of the sipping tube. A determination accuracy problem frequently arises when the animal sucks on the sipping tube rather than licking it and therefore consumes more that the presumed per lick volume, e.g. a presumed or assumed one drop/droplet per lick. 
     The second method utilizes a precision weight scale to measure the amount of liquid ingested by providing an animal weight readout. Unfortunately, stray vibrations imparted to the weight scale adversely affects accuracy of measurement. Also, such precision weight scales are extremely expensive. 
     A principal objective of our liquid ingestion monitoring system invention is to provide apparatus which precisely detects the amount of liquid ingested by a small laboratory animal over a known period of time. 
     Another objective of the present invention is to provide a precision small animal liquid ingestion detection apparatus that is relatively inexpensive to build and operate. 
     A still further object of our invention is to provide an associated computational method for determining volume of liquid ingestion by a small laboratory animal that does not rely on a presumed unit intake value. 
     Other objects and advantages of the present invention will become apparent when considering the detailed descriptions, drawings, and claims which follow. 
     SUMMARY OF THE INVENTION 
     The system apparatus of the present invention basically consists of: a liquid dispensing section (subassembly) that pumps an individual predetermined small volume (i.e., a drop/droplet) of a potable liquid from a liquid reservoir to the open end of a dispensing section delivery tube element for retention and subsequent ingestion by a small laboratory animal; a sensor section that detects each absence of a potable liquid drop/droplet previously retained at the open end of the liquid dispensing section delivery tube element following its ingestion by the small laboratory animal; and a co-operating controller section that, in response to the sensor section detecting the absence of a previously retained drop/droplet of potable liquid at the delivery tube element open end causes the liquid dispensing section to pump another liquid drop/droplet from the potable-liquid reservoir to the liquid dispensing section delivery tube element. 
     The apparatus of the present invention also includes a system resettable counter element that indicates, for the period of time involved, the number of times the system controller section causes the system liquid dispensing section to pump an individual predetermined liquid amount to the liquid dispensing section delivery tube. An accurate or precise determination of the total volume of liquid actually ingested by the animal can then be calculated using the count of the system counter element and the precisely known unit volume (i.e., drop/droplet volume) pumped into the system liquid dispensing section delivery tube element from the system potable-liquid reservoir. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically illustrates a preferred embodiment of the ingestion monitoring system of the present invention; 
     FIG. 2A is an enlarged elevation view, partially in section, of a portion of the system combined liquid delivery tube and sipping tube elements of the FIG. 1; 
     FIG. 2B is similar to FIG. 2A but relates to an alternate system liquid delivery tube and sipping tube element combination arrangement; 
     FIG. 2C is also similar to FIG. 2A but relates to a still further alternate system liquid delivery tube and sipping tube element arrangement; 
     FIG. 2D is also similar to FIG. 2A but illustrates a sensing circuit independent of the system liquid delivery tube and sipping tube elements; 
     FIG. 3 schematically illustrates serial drop/droplet presence and absence sensing signals generated by the FIG. 1 system; 
     FIG. 4 schematically illustrates an alternate sensor subassembly that may be incorporated into the FIG. 1 system invention; 
     FIG. 5 schematically illustrates an alternate liquid dispensing section that may be incorporated into the FIG. 1 system invention; and 
     FIG. 6 is similar to FIG. 4 but illustrates an alternate drop/droplet sensor subassembly that may be incorporated into the FIG. 1 system invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 schematically illustrates a preferred embodiment  10  of the ingestion monitoring system of the present invention, such being comprised of a liquid dispensing section  20 , a co-operating drop/droplet sensor section  40 , and a system conventional controller or computer section  60  that responds to the signal output of the sensor section to intermittently actuate the system liquid dispensing section. Liquid dispensing section  20  includes a liquid supply reservoir  22 , a positive displacement pump  24  which, when actuated by a control section output pulse, pumps an accurately predetermined drop/droplet volume of liquid from liquid supply reservoir  22  to liquid delivery tube  26  having a small open end  28 . Fluid flow lines  30  and  32  connect pump  24  to reservoir  22  and liquid delivery tube  26  to pump  24 , respectively. A sipping tube element  34  surrounds and is spaced-apart from liquid delivery tube  26 , and functions in-part to cause each drop or droplet D of liquid pumped into fluid flow line  30  and ultimately to the open-end  28  (see FIG. 2A) of delivery tube  26  to be retained by the end opening  36  of sipping tube  34  which is in a location accessible to the small laboratory animal A. 
     Positive displacement pump element  24  may take any one of several different particular forms including peristaltic, diaphragm, or syringe with stepping motor pump types, and preferably delivers a predetermined volume of liquid in the micro-volume range of 20 to 40 micro-liters (i.e., 0.00002 liter to 0.00004 liter) in response to each received pump input control pulse received from the system controller section  60 . Also, liquid delivery tube element  26  and sipping tube  32  of system  10  are each electrically conductive, and preferably are manufactured of a stainless steel alloy or alternatively of a metal-coated or impregnated plastic or glass. In one actual embodiment of system  10  liquid delivery tube  26  was fabricated of 15-gauge hypodermic needle stainless steel stock having a nominal internal diameter of 0.060 inches (1.52 millimeters) and an nominal external diameter of 0.072 inches (1.83 millimeters). Sipping tube element  34  in the system actual embodiment also was fabricated of stainless steel and had a nominal outside diameter of 0.3125 inch (7.93 millimeters), a nominal wall thickness of 0.020 inch (0.51 millimeters), and an end opening  36  diameter in the range of 0.040 to 0.070 inches (1.02 to 1.78 millimeters), the exact diameter selected depending upon viscosity and surface tension properties of the liquid to be dispensed. Generally, end-opening  28  of delivery tube  26  is positioned so that its edge is no farther than approximately 0.1 inch (2.5 millimeters) from the closest edge of end-opening  36  of sipping tube element  34 . 
     Drop/droplet sensor section  40  in the FIG. 1 scheme is basically comprised of an electronic clock signal generator  42 , resistor  44 , resistor  46 , capacitor  48 , and a voltage amplitude comparator device such as Schmidt trigger  50 . As shown, capacitor  48  also is electrically connected to liquid delivery tube  26  by electrical connection  52 ; sipping tube  34  is electrically connected to ground  54 . 
     When a drop/droplet D of electrically conductive liquid such as ordinary tap water is retained at end-openings  28  and  36  of liquid delivery tube  26  and sipping tube  34 , an electrical connection of capacitor  48  to ground  54  is completed through the connected conductive delivery tube, the end-retained liquid drop/droplet, and the conductive sipping tube  36 . As a result of the capacitor-to-ground connection, the system clock pulses transmitted through resistor  46  and to Schmidt trigger  50  are the low-amplitude integrated sensor output pulses  56  shown in FIG.  3 . However, when small laboratory animal A takes and ingests the liquid drop/droplet D from the end opening  36  of sipping tube  34 , the capacitor-to-ground connection is broken and the resulting charging of capacitor  48  causes the sensor clock signals inputted to device  50  to be the high-amplitude pulses  58  of FIG.  3 . Whenever an increasing clock signal voltage amplitude change is sensed by circuit trigger  50  a sensor output pulse is inputted to conventional controller  62  to cause subsequent actuation of pump  24  for a single output stroke and actuation of counter  64  for a single digit count increase. 
     As shown in FIG. 2A, the longitudinal axes of liquid delivery tube  26  and sipping tube  34  preferably coincide. However, in some applications of ingestion monitoring system  10  it may be advantageous to offset those axes slightly with respect to each other as shown in FIG.  2 B. Also, and as shown in FIG. 2C, in still other embodiments of ingestion monitoring system  10  it may be advantageous to discharge liquid from delivery tube  26  through a side-wall opening or hole  29  rather than through a tube end-opening  28 . FIG. 2D illustrates an embodiment where deliver tube  26  and sipping tube  34  are formed from non-conductive material such as plastic and a pair of spaced electrodes  35   a  and  35   b  extend down the outside of sipping tube  34  and terminate on opposite sides of end opening  36 . In some instances electrodes  35   a  and  35   b  may project into the space between end openings  28  and  36  of liquid delivery tube  26  and sipping tube  34 . Of course, one or both electrodes  35   a  and  35   b  could be positioned inside of sipping tube  34 . Also, only one electrode may be used where one of the delivery tube  26  and the sipping tube  34  are formed from a conductive material. 
     FIG. 4 schematically illustrates details of an alternate arrangement for the construction of the system sensor section. Such is referenced by the numeral  70  and its principal components are a light source such as separately energized light emitting diode (LED)  72  positioned to one side of sipping tube  34  and a conventional photosensor diode or photo transistor cell  74  positioned to receive light rays from LED  72  that are either transmitted through or back-scattered from the lower extreme of sipping tube  34 . In such alternate arrangement tube elements  26  and  34  need not be electrically conductive but sipping tube  34  must be optically transparent. Conventional photosensor diode cell  74  is selected so that its sensitivity results in the inputting of a reduced voltage signal to system controller/computer  62  whenever it senses an increase in light ray level of intensity due to the lack of light transmission obstruction by the absence of a liquid drop/droplet D otherwise retained in the zone between the free ends of liquid delivery tube  28  and sipping tube  34 . The FIG. 4 type of invention ingestion monitoring system is especially useful in applications wherein the liquid being dispensed is electrically non-conductive such as occurs when distilled water is to be dispensed through system delivery and sipping tubes  26  and  34 . 
     FIG. 5 illustrates another form of liquid dispensing section for ingestion monitoring system  10 . Such is referenced by the numeral  80  and is comprised of liquid supply reservoir  82 , liquid metering valve  84 , and a co-operating liquid delivery tube  28  and sipping tube  34  combination. Liquid supply reservoir  82  differs from liquid supply reservoir  22  in that it must maintain the fluid within at a constant pressure at all operating times. Metering valve  84  is normally closed but when actuated by a command signal received from system controller/computer section  60  is opened for a unitary period of time having a duration that is fixed by the controller/computer section. Thus, knowing the reservoir constant pressure and the time duration of the valve open period, the volume of the liquid drop/droplet flowed from liquid supply reservoir  82  to liquid delivery tube  26  can be precisely predetermined as in the case of actuation of liquid pump  24 . 
     A still further system drop/droplet sensor section construction variation  90  is schematically illustrated in FIG.  6 . In the FIG. 6 arrangement bundles  92  and  94  of optic fibers are utilized to transmit light from a light source such as LED  96  to the zone occupied by the open ends of system tubes  26  and  34  and from that end zone to photovoltaic cell element  98 , respectively. 
     Various changes may be made to the shape, proportionate size, materials of construction of the invention elements described in detail in the foregoing detailed description, and substitutions may be made for the various disclosed invention elements with their functional equivalents, without departing from the meaning, scope, or intent of the claims which follow.