Reflex Cardio-inhibition in "Shock." 



9i 



without lowering the general pressure. This was accomplished 

 by ligation of the two carotid and two vertebrals. It is appreci- 

 ated that even this procedure is incapable of absolutely prohibiting 

 blood from passing to the medulla in dogs on account of the great 

 collateral supply and anastomosis. However, the decrease in 

 blood supply by this method yielded similar results to those ob- 

 tained in hemorrhage and a reestablishment of the circulation 

 resulted in a return of the threshold to the normal if the duration 

 of the anemia was not too prolonged. This was comparable to 

 the effect of transfusion following hemorrhage. The third series 

 represents an amplification of the previous work on the effect of 

 trauma upon the cardio-inhibitory reflex. In the early experi- 

 ments there appeared to exist a parallelism between the blood 

 pressure following trauma and the threshold value for the reflex 

 in the sense that low pressure brought about a high threshold and 

 high pressure, a low threshold. A further study has brought about 

 the conviction that this relationship may exist but that other 

 factors, at present insufficiently studied, alter the results obtained. 

 Following intestinal trauma blood pressure may be high or low 

 according to the initial degree of vaso-constriction; 1 the threshold 

 may be heightened or lowered when the blood pressure is either 

 high or low. One might explain this apparent discrepancy in the 

 findings by the assumption of a factor of inhibition acting inde- 

 pendent of the blood pressure and altering the threshold reflexly 

 It is possible, however, that determinations of carotid pressure 

 may not represent accurately the pressure and volume flow of 

 blood in the medullary capillaries. Thus vaso-constriction of the 

 arterioles in the medulla would result in an anemia of that part 

 although the pressure in the carotid might still be normal. It is 

 our intention to examine more closely this phase of the matter. 

 1 Muns, Proceedings Soc. Exp. Biol. Med., 1915, XII. 87. 



