6o 



Scientific Proceedings (88). 



(Frequent readings between 3.13 and 

 4.36. Change between successive read- 

 ings never equal to a whole unit of 

 stimulation.) 



4.37 Intestines withdrawn and 



manipulated. 



4.38 Threshold 16.8 Z units. 

 Threshold gradually rose. 



5.07 Threshold 20.3 Z units. 



5.08 Intestines returned. 



5.16 Threshold 14. 1 Z units. 

 6.00 Threshold 14.5 Z units. 



The changes in threshold I have found to bear no relation to 

 changes in blood pressure. The threshold may return to its 

 original level with a lower blood pressure than at the time it 

 went up. 



The threshold of crossed-extension, obtained by stimulating 

 the same nerve and recording the contractions of the quadriceps 

 group of muscles, has a much more variable threshold than the 

 flexion reflex before manipulation of the intestines, but quite 

 evident changes in this threshold follow manipulation (Exp. of 

 July 24). I have found the reflex in a number of cases to disappear 

 for a few moments or longer as the result of the manipulation. 

 The high threshold produced is less likely to return to its original 

 level than the flexion threshold. The rise in threshold is just as 

 prompt as in the case of flexion. In one case I have found a 

 complete return to the original threshold, but only after an 

 interval of an hour and a quarter after the manipulation of the 

 intestines had ceased. 



These results are of interest in connection with the present 

 work on the shock problem. Pike has emphasized recently the 

 probability of some physical injury to the central nervous system 

 in shock. W. T. Porter has done the same in his theory of fat 

 embolism. The injury I have studied is better described as 

 physiological rather than physical. The prompt and complete 

 return of threshold to its original value in some cases indicates 

 that the injury cannot be so gross as the fat embolism of Porter. 

 It is an inhibition, in the words of Meltzer, or an increase in synap- 

 tic resistance, as Cannon has recently referred to it. 



The problem which immediately suggests itself is whether it 



