310 THE CIRCULATION IN THE BLOOD-VESSELS [CH. XXI. 



fall of the oncograph lever, showing that the kidney 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 (which is taken as a control to be sure the 

 changes are not otherwise produced) 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 the kidney. We may, however, say in passing 

 what a very important experimental method plethysmography is 

 becoming. Since the introduction of air oncometers, the method is 

 remarkably easy to apply, and it is now part of the routine practice 

 of physiologists, when they are investigating the action of a drug, 

 or of a nerve, on any organ, to record its volume changes by the 

 plethysmographic method. Thus, the salivary glands, lobes of the 

 liver or lung, the limbs, the kidney, spleen, a coil of intestine, etc., 

 can all be easily enclosed in an appropriately shaped gutta-percha 

 box, covered with a glass plate made air-tight with vaseline. There 

 are always two openings to such a box, one to allow the vessels and 

 nerves to enter (leakage of air around these is prevented by packing 

 with cotton-wool soaked in vaseline) ; the other opening is filled up 

 with a piece of glass tubing which is connected by an indiarubber 

 tube to the recording apparatus. The most delicate of the volume 

 recorders is the bellows-recorder of Brodie (see p. 152) and the 

 piston recorder of Hiirthle; a Marey's tambour is not so sensitive, 

 and, moreover, it is a recorder of pressure rather than of volume only. 



Of all the oncometers, I am inclined to believe that the intestinal 

 oncometer is the most instructive, because the coil of intestine under 

 observation gives a truer record of what is occurring in that important 

 area called the splanchnic area, than any other abdominal organ. 



Pathological Conditions. 



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). 



It is almost impossible to over-estimate the importance of the 

 study of vaso-motor phenomena, as a means of explaining certain 

 pathological conditions; our knowledge of the processes concerned 

 in inflammation is a case in point. 



Disorders of the vessels due to vaso-motor disturbances are 

 generally called angio-neuroses. Of these we may mention the 

 following : 



Tache cercbrale is due to abnormal sensitiveness of the vascular 

 nerves ; drawing the finger-nail across the skin causes an immediate 

 or at least a red mark that lasts a considerable timo. At one 



