504 ELECTRO-PHYSIOLOGY CHAP. 



the current, for when the vaso-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 antenna is induced with a consequent 

 marked increase of aortic pressure. Here, as during dyspnoeic 

 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 Wood-pressure is at 

 its maximum. 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, anaemia 

 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. 

 It is 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, 



