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PHYSIOLOGY 



CHAP. 



more ischaemic and cooler than the healthy linib on the opposite 

 side (Goltz and others). This means that the muscle cells, or 

 peripheral ganglionic elements, may, independent of the nerve 

 centres, acquire a degree of tonic contraction in excess of the 

 normal. On the other hand we know that even excised organs, 

 e.g. the dog's kidney, artificially circulated, exhibit with the 



FIG. 158. Plethysmogram of forearm, obtained by connecting the cylinder, A, B, of plethysmo- 

 graph with a Marey's writing tambour. (Mosso.) .The rotating drum moves at uniform speed. 

 The experiment was performed in an iron room, where the air could be compressed to various 

 measurable pressures. Each tracing, in addition to the plethysmograms of the pulse, shows 

 the slow oscillations in volume of the forearm which depend on the oscillations of vascular 

 tone. 1, Tracing made before compression of air; 2, at 160 mm. Hg compression; 3, at 

 100 mm. Hg ; 4, at 80 mm. Hg ; 5, at 50 mm. Hg ; 6, at ordinary barometric pressure ; 7, two 

 minutes alter return to ordinary barometric pressure ; 8, a quarter of an hour later. 



plethysniographic method constant irregular oscillations of 

 volume, which obviously depend on oscillations of tone in the 

 renal vessels (Mosso, 1874). 



A similar effect was noted by Bernstein in the amputated 

 paw of the dog. So, too, the work of Bayliss (1901), on the 

 reaction of certain blood-vessels to changes of blood pressure, 

 shows that the vascular muscles are capable of altering their 

 tone independent of the nervous system. Bayliss found on 

 recording the changes in volume of the hind limb of an animal, 



