VASOMOTOR REFLEXES 363 



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In forty-six cases out of sixty-two in total, weak stimulation 

 produced a fall or a fall followed by a rise, and strong stimula- 

 tion caused a rise or a rise followed by a fall. A typical response 

 is shown in figure 6. 



The animal was under ether and the thorax was very wide 

 open in the middle line in order to eliminate the disturbance 

 from increased respiratory movements. Figure 7 shows a similar 

 response under chloroform. 



In the remaining sixteen cases the response was either a fall 

 or a rise through all strengths of stimulation which we used, and 

 the different effects with weak and strong stimulation were not 

 observable. 



Thus it does not seem to us unreasonable to conclude that 

 weak stimulation of the central stump of the cut nerve produces 

 usually a fall of blood-pressure and a strong stimulation produces 

 usually a rise. 



From these conclusions it may naturally be understood that 

 from the threshold of stimulation up to a certain point the fall 

 of blood-pressure increases with the development of the strength 

 of stimulus, and then the fall gradually decreases until a neutral 

 point is reached, where the vasoconstriction and dilatation just 

 counterbalance each other, and finally the rise appears, which 

 increases usually with the increase of the strength of stimulus, 

 but cannot continue very long, since powerful stimuli would 

 elicit vigorous reflex movements of the animal and obscure the 

 true vasomotor reactions unless indeed the animals were deeply 

 under curare. As we have been unable so far to find any at- 

 tempt by previous investigators except Stiles and Martin'* ° to 

 describe this rather peculiar course of vasomotor responses, we 

 though it worth while to emphasize it in this place (fig. 8). 



In our experiments we have employed also stimuli of other 

 kinds than electric induction shocks, namely, mechanical, ther- 

 mal, and chemical. In this series thirty-eight out of sixty-seven 

 stimulations were effective, and of these thirty-five caused a fall 

 of blood-pressure and only three produced a rise. As the cali- 

 bration of these stimuli was not so practicable as with induction 

 shocks, we cannot draw any very positive conclusions, but we 



