THE PLETHYSMOGRAM OF THE KIDNEY 277 



This is an exceptionally good method for direct observation of the vaso- 

 motor changes. 



24. The Plethysmogram of the Kidney. Anesthetize a dog or cat, 

 see Experiments 12 and 19 above, and take continuous blood-pressure 

 tracings. Now open the abdominal wall by an incision along the median 

 line, expose the left kidney and carefully dissect off its capsule, taking 

 care not to injure its artery and vein. Enclose the kidney in the renal 

 onkometer and carefully seal with vaseline and cover with omentum. 

 Connect it with a delicate volume recording apparatus. Brodie's bellows 

 recorder or a large air tambour is the best for this purpose. Adjust the 

 recording apparatus in the vertical line with the manometer and signal 

 pens. 



Stimulation of the nerves which affect general blood-pressure through 

 the medium of the heart will produce changes in the volume of the kidney 

 in the same direction as the blood-pressure. Stimuli which give varia- 

 tions of the blood-pressure without direct change in the heart itself affect 

 the volume of the kidney independent of the blood-pressure : 



a. Dissect out and stimulate the splanchnic nerves just where they 

 pass through the pillars of the diaphragm. They cause vaso-constriction 

 in the kidney without sharply affecting the blood-pressure. 



b. Stimulate the depressor nerve, or the central end of the divided 

 vagus. The volume of the kidney will increase though the general blood- 

 pressure decreases, showing that the fall of blood-pressure is due to 

 peripheral vascular dilatation. 



c. Stimulate the peripheral end of the divided vagus so as to slow or 

 even completely to stop the heart. The sharp fall in blood-pressure is now 

 accompanied by decrease in the volume of the kidney, showing that the 

 kidney volume is merely passively following the blood-pressure. 



