NERVOUS CONTROL OF THE BLOOD-VESSELS 993 



Schafer's plethysmograph (Fig. 462), which can be adapted to almost any organ of 

 the body, is made of vulcanite * previously moulded to the size of the organ whose 

 volume is the object of investigation. In one side of the box a depression is left sufficient 

 to accommodate easily the vessels, nerves, or ureter going to the organ. The oncometer 

 is covered with a glass lid which is made air-tight by means of vaseline, the space 



R 



FIG. 462. Diagram of Schafer's air plethysmograph. 



between the lid and the vessels being also packed with cotton-wool and vaseline. A 

 glass tube is fixed into one corner of the plethysmograph and leads to a piston recorder or 

 tambour. Every variation in the volume of the organ causes a movement of air into or out 

 of the oncometer and thus gives rise to a corresponding movement of the recording lever 



Blood- pressure 



Kidney volume 



FIG. 463. Simultaneous tracings of carotid blood-pressure and volume of kidney. 

 Between x and x the peripheral end of the divided tenth dorsal nerve was 

 stimulated. Time-marking = seconds. (BRADFORD.) 



The kidney being placed in some such apparatus, a cannula is also placed 

 in the carotid artery and connected with a mercurial manometer, so that 

 two tracings are obtained at the same time on the moving blackened surface. 

 In the figure given (Fig. 463), the upper curve represents the carotid blood- 



* A very good material for this purpose is ' Stent's composition,' used by dentists 

 for taking a mould of the jaw in fitting artificial teeth. 



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