992 



PHYSIOLOGY 



(3) An increased velocity of blood- flow will, if the part be normally 

 below the temperature obtaining in the central organs of the body, raise its 

 temperature, and vaso- dilatation can thus be detected by the application of 

 the hand or of a thermometer. 



(4) Any of the methods mentioned in a previous chapter may be used 

 to determine the velocity in the arteries going to the part, and an increased 

 velocity may be interpreted as due to vaso-dilatation. 



(5) The increased flow through the part may be detected by cutting 

 the main efferent vein and measuring the total volume of blood which flows 

 from it in a given time. 



Of these methods the two most used are those based on determination 

 either of the volume of the part, or of the venous outflow from the part. 



to oncometer 



FIG. 460. Diagram of oncometer. 



FIG. 461. Diagram of oncograph. 



A fallacy may, however, arise, unless means be taken to ensure that the 

 general arterial pressure remain constant during the experiment. A rise 

 of general blood-pressure will cause an expansion of the vessels and of the 

 part supplied, and also increased velocity of blood-flow through the part. 

 In all cases therefore where it is desired to investigate the conditions of the 

 local circulation, it is necessary to combine a determination of the general 

 blood-pressure with some means of estimating changes in the local conditions. 

 We may take as an instance an experiment on the blood-supply to the 

 kidney. 



For this purpose we may use a kidney plethysmograph or oncometer. The structure 

 of Roy's oncometer is shown in Fig. 460. The oncometer is a metal capsule, the two 

 halves of which are hinged together and come in contact at the whole of their circum- 

 ference except at Ti, where a small depression is left in each half for the passage of the 

 kidney vessels and ureter. A piece of peritoneal membrane is attached to the rim of 

 each half of the oncometer, the space between this and the brass capsule being filled 

 with warm oil. The kidney rests in the oncometer on this bed of warm oil, from which 

 it is separated by a membrane. A tube leads from the cavity between the brass capsule 

 and membrane to a registering apparatus, or oncograph (Fig. 461), which is a piston 

 recorder containing oil. Any swelling of the kidney will drive oil out of the oncometer 

 into the cylinder of the oncograph and so raise the piston, the excursions of which are 

 recorded by a lever writing on a blackened surface. 



