189 



CHAPTER XVIII 



THE KIDNEY. DEMONSTRATION OF AN ONCOMETER EXPERIMENT 



In investigating the mode of action of any organ or part of the body 

 one of the first things we require to know is how its blood flow is 

 modified under different conditions, in order that we may be able to 

 correlate these changes with other functional activities simultaneously 

 observed. There are several methods open to us by means of which 

 we may observe changes in vascularity of an organ. In many cases 

 simple inspection by revealing differences in colour is able to show us 

 that there is more or less blood in the organ, but this method can 

 only show us gross changes. A second plan is to measure the quan- 

 tity of blood issuing from the organ, variations in the rate of outflow 

 giving a measure of the amount of blood passing through the organ. 

 This is one of the most satisfactory methods if we are working upon 

 an excised organ and circulating defibrinated blood through it by tying 

 a cannula into its main artery. The third and the most valuable 

 is that known as the plethysmography method. Here the changes 

 in volume are directly measured by confining the organ in sonic 

 enclosed space and then recording the amount of air or of llui 

 displaced from this space as the organ expands or contracts. 



The general plan adopted in such an experiment may be bi I 

 illustrated by one upon the kidney. 



The original form of apparatus, as invented by Roy for experiments upon 

 the kidney, consists of a metal box, in which the kidney is placed, called an 

 oncometer (bulk measurer), and a piece of recording apparatus termed an 

 oncograph (bulk recorder). The form of the oncometer is shown in tig. 152, 

 and a diagram of its general principle in fig. 158. It consists of an ellipsoidal 

 metal box made to open by a hinge. Each half consists of a double metal 

 box (oc and ic, fig. 153), the one fitting tightly within the other. To prepare \\ 

 for use each inner half is removed and a sheet of sheep's peritoneal membrane, 

 5i, is fitted over it, and its edges gummed down to the outer surface of the 

 capsule, to make an air-tight joint. The membrane is fitted, on verj loosely, 

 and thus allows free movement inwards and outwards. The inner bos is 

 then replaced in the outer, to which it is tightly clamped by the screw -,. 

 Both sides are now filled with oil, so as to fill up the spaces a and B between 

 the peritoneal membrane and the inner cases, the membrane being raised 

 meanwhile so that when the instrument is closed there is sufficient space 1< fl 



