NERVOUS CONTROL OF THE BLOOD-VESSELS 1117 



For this purpose we may use a kidney plethysmograph or onco- 

 meter. The structure of Roy's oncometer is shown in Fig. 465. 

 The oncometer is a metal capsule, the two halves of which are hinged 

 together and come in contact at the whole of their circumference 

 except at h, where a small depression is left in each half for the passage 

 of the kidney vessels and ureter. A piece of peritoneal membrane is 

 attached to the rim. of each half of the oncometer, the space between 

 this and the brass capsule being filled with warm oil. The kidney 

 rests in the oncometer on this bed of warm oil, from which it is separated 

 by a membrane. A tube leads from the cavity between the brass 



FIG. 4G7. Diagram of Schafer's air plethysmograph. 



capsule and -membrane to a registering apparatus, or oncograph (Fig. 

 466), which is a piston recorder containing oil. Any swelling of the 

 kidney will drive oil out of the oncometer into the cylinder of the 

 oncograph and so raise the piston, the excursions of which are recorded 

 by a lever writing on a blackened surface. 



Schafer's plethysmograph (Fig. 467), which ca,n 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 between the lid and the vessels being also packed with cotton- 

 wool and vaseline. A glass tube is fixed into one corner of the plethys- 

 mograph 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. 



* 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. 



