395 RELATION OF RESPIRATION TO OTHER PROCESSES [oil. XXVII. 



an organ or tissue per gramme per minute is called its coefficient of 

 oxidation. 



Measurement of Coefficient of Oxidation. The method adopted 

 depends upon whether the observer desires to ascertain the 

 coefficient at a particular moment of time, or its average value over 

 a considerable period. If the former is desired, it is necessary: 

 (1) to estimate the gases in the blood going to and emerging from 

 the organ ; this is performed by the chemical method of expelling the 

 oxygen and carbonic acid from samples of the arterial and venous 

 blood by means of potassium ferricyanide and tartaric acid respec- 

 tively (see p. 364); (2) to determine the amount of blood passing 

 through the organ in a given time, say one minute ; and (3) at the 

 conclusion of the experiment the organ is weighed, so that the 

 gaseous exchange per gramme can be calculated. 



FIG. 308. Tracing to illustrate Brodie's method of ascertaining the rate of blood-flow through 

 an organ. For explanation see text. 



The rate of the flow of blood through an organ may be ascertained, 

 either by directly measuring the venous blood as it emerges from 

 the organ, or by a very simple method introduced by Brodie ; the 

 organ is enclosed in an oncometer connected to a bellows recorder ; the 

 issuing vein is compressed for about a second, and the blood flowing 

 into the organ causes it to expand; the lever of the recorder rises 

 quickly or slowly according to the rate at which the blood is flowing 

 into the organ. The recorder is first calibrated by injecting half a 

 cubic centimetre of water into the tubing leading to it, and the 

 position of the lever at rest, and that which it occupies when the 

 oncometer is distended by half a cubic centimetre of water are 

 marked continuously by two fixed writing-points. In the accom- 

 panying figure, obtained from an experiment on a kidney, these two 

 lines are lettered A and B. The surface travels at a quick rate, and 

 the time-tracing T shows thirtieths of a second. The line C is traced 

 by the oncometer lever. 



