398 EXCRETION 



LABORATORY EXPERIMENTS IN EXCRETION. 

 PHYSIOLOGICAL REACTIONS 



i. The Relation of Blood Flow through the Kidney to the Secre- 

 tion of Urine. Properly to check this experiment one should make 

 three determinations: i, the general blood pressure; 2, the volume of the 

 kidney; 3, the amount of urine secreted. Anesthetize a dog and arrange the 

 apparatus for taking the blood pressure as directed in experiment 19. Prepare 

 a renal onkometer, see figures 301 and 302, and an onkograph for recording 

 the variations in the volume of the kidney. The renal onkometer consists of 

 a double metal box to fit the form of a kidney. The inner halves of this box 

 should be covered so loosely with very thin sheet rubber that the rubber can 

 be fitted into the bottom of the cup without undue tension. The rubber must 

 be sealed to the outer edges of this inner cup with rubber cement and allowed 

 to dry. When it is completely dried the inner cup should be adjusted to the 

 outer, and the spaces enclosed by the rubber sheet filled with water. Or 

 the onkometer may be closed with parchment and filled with oil as de- 

 scribed in experiment 23 on the Circulation. The half of the onkometer 

 that comes against the wall of the body cavity of the animal should be 

 completely closed with a stopper before the instrument is adjusted to 

 the kidney. Now adjust the onkometer to the kidney, taking care to 

 place the renal arteries, veins, and ureter in the tube in such a way as not 

 to compress them. Fill the outer cup with water and connect this cavity 

 by a two-way cannula with the recording onkograph. In practice it is more 

 satisfactory if one introduces between the onkometer and onkograph an over- 

 flow bottle or bulb, adjusted to maintain the constant pressure on the kidney. 

 This direction varies from the usual one in that rubber sheeting instead of 

 parchment is used to cover the inner cup of the onkometer, a method that 

 permits the use of water instead of oil. 



Isolate and insert a small cannula into the ureter. This cannula should 

 be clamped in a stand at a level as little above that of the kidney as possible. 

 The urine secreted may be collected in a 10 c.c. graduated cylinder and 

 measured at intervals of 5 or 10 minutes. Or, if the outflow is scanty, it may 

 be allowed to drop on a tambour recording apparatus, the rate of dropping 

 being indicative of the rapidity of secretion. 



Determine the normal rate of secretion of a dog under constant anesthesia. 

 The anesthesia should be medium to light, but should be kept very uni- 

 form so as to maintain a strong blood pressure. Note the effect on secre- 

 tion and the corresponding effect on blood pressure and the kidney volume 

 produced by vagus inhibitions. Section the vagus nerves and produce in- 

 hibition by stimulating the peripheral end of the vagus. In this instance 

 there are no reflexes to complicate the experiment, so that the fall in blood 



