504 ELECTRO-PHYSIOLOGY CHAP. 



the current, for when the vase-motor centre is excited, and the 



pressure in the aorta rises, in consequence of dyspnoea, the natural 



concomitant is fall of pressure in the small arteries and capillaries 



of many peripheral organs, and the stomach in particular, where, 



as well as in the viscera, the vessels are narrowest. Similar results 



are obtained with another experiment on the rabbit, in which, by 



clamping the four arteries which supply the head, by S. Mayer's 



method (85), cerebral anaemia is induced with a consequent 



marked increase of aortic pressure. Here, as during dyspnceic 



excitation of the vaso-motor centres, the stomach current again 



after a brief positive fore-swing- declines very markedly, being 



as a rule already reversed at a time when the Hood-pressure is at 



its maxiimun. If the clip is removed before the centre has 



become permanently injured, the blood-pressure returns rapidly 



to its normal level, but the current requires much longer to 



recover its original proportions. If, on the other hand, anemia 



is prolonged till the blood-pressure is at " paralytic " level, owing 



to the paralysis of the centre, the ingoing direction of the current 



does indeed gradually reassert itself, but never approximates to 



its original strength, exhibiting at most a deflection of a few 



gradations. 



In view of the last-named results, in which venous action of 

 the blood passing into the stomach of the slightly curarised, 

 artificially breathing animal seems to be wholly excluded, the 

 presumption gains ground that local decline of pressure in con- 

 sequence of diminished arterial blood-supply is in dyspnoea also the 

 proper cause of the negative variation. We should then expect 

 an opposite effect, i.e. increase of entering current, when pressure 

 was raised in the vascular system. One way in which this can 

 be accomplished is by transfusion of fluids at greater densities. 

 5 known from the investigations of Cohnheim and Lichtheim 

 (86) that even when enormous quantities of 0'6 % salt solution 

 is injected into the jugular vein of rabbit or dog, the blood- 

 pressure undergoes no particular increase, and remains fairly 

 normal. "There was no question of rise in ratio with the 

 densities injected. Marked increase of pressure only occurred 

 during an experiment when the initial pressure had been excess- 

 ively low ; in this case the infusion of fluid produced rapid rise 

 of blood-pressure to the mean." On the other hand, a marked 

 acceleration of the circulation was obvious in all these experiments, 



