3IO THE CIRCULATION IN THE BLOOD-VESSELS. [CH. xxi. 



plate, made air-tight with vaseline, except where it communicates 

 by a tube with a Marey's tambour, gives a far more delicate record 

 of the splenic alterations of volume than the oil oncometer. 



If now we are investigating the action of the anterior root of 

 eleventh thoracic nerve on the vessels of the kidney, a tracing is 

 taken simultaneously of the arterial blood-pressure in the carotid, 

 and of the volume of the kidney by the oncometer. On stimu- 

 lating the nerve rapidly, there is a slight rise of arterial pressure, 

 but a large fall of the oncograph lever showing that the kidney 



Fig. 290. Diagram of Roy's Oncometer. a, represents the kidney enclosed in a metal box, 

 which opens by hinge/; 6, the renal vessels and duet. Surrounding the kidney are 

 two chambers formed by membranes, the edges of which are firmly fixed by being 

 clamped between the outside metal capsule, and one (not represented in the figure) 

 inside, the two being firmly screwed together by screws at h, and below. The mem- 

 branous chamber below is filled with a varying amount of warm oil, according to 

 the size of the kidney experimented with, through the opening, then closed with the 

 plug t. After the kidney has been enclosed in the capsule, the membranous chamber 

 above is filled with warm oil through the tube e, which is then closed by a tap (not 

 represented in the diagram) ; the tube d communicates with a recording apparatus, 

 and any alteration in the volume of the kidney is communicated by the oil in the tube 

 to the chamber d of the Oncograph, fig. 291. 



has diminished in volume. It is evident that there must be an 

 active contraction of the arterioles of the kidney, causing it to 

 diminish in size, for the blood-pressure tracing shows that there 

 is no failure of the heart's activity to account for it. 



We shall return to the subject of the oncometer in connection 

 with the spleen and kidney. 



The vaso-motor nervous system is influenced to some extent by 

 conditions of the cerebrum, some emotions, such as fear, causing 

 pallor (vaso-constriction), and others causing blushing (vaso- 

 dilatation). 



