CARDIOVASCULAR CHANGES DURING CEREBRAL ANEMIA 31 



indefinitely. The difficulty of inducing fatigue of the central vasomotor 

 cells under normal conditions has been discussed in various connections 

 by W. T. Porter (100), (101). 



The experiments already described in this series on repetition of 

 occlusion have been complicated by the infliction of lesions in the 

 splanchnic system so that the actual ability of the animals to with- 

 stand repeated occlusions, and the effect of this procedure on the anemic 

 response, was not clear. Furthermore, not more than six or eight suc- 

 cessive occlusions at most were obtained. Accordingly, in five cats 

 the effects of repeated occlusion were tested. Occlusion was done and 

 when the final spontaneous fall of pressure occurred, the clamps were 

 promptly released and recovery awaited. The corneal reflex was used 

 as before as an index of returned bulbar activity. With its elicitation 

 clamps were again adjusted on the head arteries, and this process 

 repeated several times. 



If the occlusion period was not too long maintained in any one clos- 

 ure, it was possible to repeat the procedure practically indefinitely. 

 In the three most striking experiments, cats 45, 46 and 48, the experi- 

 ments had to be halted arbitrarily because of extraneous reasons, the 

 time consumed being too long. Cat 45 yielded 18 successive occlu- 

 sions (fig. 4); cat 46, 13 successive occlusions; cat 49, 11 successive 

 occlusions. These experiments lasted over 3 hours in addition to the 

 time necessary for the preliminary operative manipulations which 

 always consumed over half an hour. Cat 46 was intact, cat 45 had 

 suffered double vagotomy, and in cat 48, (fig. 5A) both stellate ganglia 

 had been removed. No marked difference in the behavior of these 

 cats under the test could be noted. In fact, the cats showed a remark- 

 able constancy in behavior. The characteristic occlusion time 2 

 to 4 minutes in each individual was retained with considerable uni- 

 formity throughout each series. Furthermore, the time needed for 

 recovery of the bulbar functions after release of the arteries was almost 

 uniform for each cat examined. The recovery time which, on the whole, 

 may be said to vary directly with the occlusion time, did not in all 

 cases follow this relation. Cat 46, which gave a constant occlusion 

 time of 2 minutes usually showed a recovery of a corneal reflex 

 within 7 . minutes subsequently. Cat 45, however, (vagotomized) 

 invariably showed a 20-minute interval between occlusions. In this 

 interval a well-marked recovery of blood pressure was noticeable and, 

 with the return of respiration, blood pressure rose at least from 60 to 

 80 mm. above the level after occlusion, before a corneal reflex was 



