50 



Scientific Proceedings (96). 



The experiments described here were done on cats. Etheri- 

 zation and tracheotomy were routine procedures. Some of the 

 cats were decerebrated, after which no more ether was necessary. 

 The two common carotid and two vertebral arteries were isolated 

 in the neck so that they might be ligated temporarily or perma- 

 nently. Blood pressure was taken from the left carotid artery 

 and the respiratory movements recorded by a Crile stethograph 

 and a Verdin tambour. Blood for the estimation of the carbon 

 dioxide was drawn from the femoral artery, and the estimations 

 were made by the Van Slyke method. Changes in the volume of 

 blood flowing through the medulla were brought about by occlud- 

 ing the cerebral arteries. Control samples of blood were taken 

 at the beginning of each experiment. Other samples were taken 

 during the period of occlusion of the cerebral arteries and after 

 the release of these arteries and the restoration of the cerebral 

 circulation. In some of the experiments, the arteries were never 

 occluded, but changes in the blood flow to the medulla were pro- 

 duced by successive small hemorrhages of eight to ten cubic 

 centimeters each. Pulse counts in some of these experiments 

 were made by Miss Ethel Wickwire. 



Simple occlusion of the cerebral arteries was sufficient to pro- 

 duce severe dyspnoea in some animals, but in others, dyspnoea 

 appeared only after a considerable quantity of blood had been 

 drawn. In all animals, the effects of the occlusion became more 

 and more severe as more and more samples of blood were drawn. 

 Hemorrhage alone, if carried sufficiently far, is followed by 

 dyspnoea. Any injury to the spinal cord which prevents the 

 compensatory rise of systemic blood pressure is followed by more 

 severe dyspnoea on occlusion of the cerebral arteries than other- 

 wise results. 



The changes in the total carbon dioxide of the blood attending 

 occlusion of the cerebral arteries are shown in the following table. 



It is seen that the total carbon dioxide of the blood falls during 

 each occlusion and rises again during each period of free flow 

 of blood through the medulla until about forty per cent, of the 

 total volume of the circulating blood has been drawn off for analy- 

 sis. Beyond this point, there is a fall in the concentration of the 

 carbon dioxide of the blood as each sample is drawn. Hemorrhage 



