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Scientific Proceedings (125) 



is completely interfered with and cerebral anaemia with the at- 

 tendant anaemic rise of blood-pressure ensues rapidly. The high 

 level of blood-pressure is maintained until the fall to the spinal 

 level of pressure indicates the failure of bulbar function. If the 

 occlusion has not been carried on for too long a time, release of 

 the head arteries with the maintenance of artificial respiration 

 results, eventually, in restoration of the bulbar and cerebral func- 

 tion, the degree of restoration of function depending on the 

 amount of injury that has been inflicted by the occlusion. 



In our experiments, the beginning of the fall in blood-pressure, 

 after the anaemic rise induced by occluding the head arteries, was 

 the signal for the restoration of cerebral circulation, and the re- 

 turn of the blood-pressure to the previous level (or nearly so), 

 together with the return of an active corneal reflex were usually 

 the criteria for the beginning of the next occlusion of the head 

 arteries. Artificial respiration was constantly maintained after 

 the beginning of the first occlusion. 



By employing this technique a number of occlusions (up to 

 about thirty) can be made before there is a lack of response from 

 the medulla to cerebral anaemia. In a large number of cases, 

 after the first few occlusions, the curve of the anaemic rise has 

 been observed to dissociate into two parts, each occupying about 

 half the time which an undissociated curve would occupy, as re- 

 ported by Mrs. Winkin. This type of dissociation curve we have 

 obtained, however, not only in normal animals, but with equal 

 success in the animals in which epinephrin secretion had been 

 suppressed or abolished. 



Moreover, animals in which adrenal function had been greatly 

 interfered with or abolished by the operations above mentioned 

 are able to respond in the usual manner to as many occlusions of 

 the head arteries as normal animals. We have found that the 

 number of definite responses to cerebral anaemia is largely de- 

 pendent upon the general blood-pressure level existing just be- 

 fore the occlusion and that when this has fallen to spinal level 

 so that no rise in blood-pressure can be obtained on occlusion of 

 the head arteries, it is possible to obtain good responses by rais- 

 ing the basal level through injection of Ringer's solution, so long 

 as the Ringer's solution is capable of sustaining a higher level of 

 blood-pressure. But when a condition is reached when the 

 blood-pressure improvement is transient, the usual responses are 



