8o SCIENCE PROGRESS 



that it could only be brought about by the mediation of the 

 vagus. 



Of course many other factors — chemical, mechanical and 

 thermal, as well as nervous — must play some part in producing 

 the strong acceleration of the heart consequent on severe 

 exercise, when the frequency may become in man 170 or 180 

 per minute, and when the duration of the systole as well as 

 that of the diastole is shortened. To answer our question we 

 require to know whether it is to them or to nervous factors 

 only that the acceleration is due which occurs with involuntary, 

 reflexly produced, muscular movements for the regulation of 

 temperature, such as shivering, evidence of which I have 

 obtained from one or two medical undergraduates who kindly 

 took their pulse-rates several times under conditions which 

 induced shivering for comparison with what it was before the 

 shivering commenced. Since the shivering cannot be made to 

 begin at a precise moment, we cannot ascertain in the same 

 way as for voluntary movements whether the heart-acceleration, 

 as well as the movement itself, is brought about by the agency 

 of the central nervous system ; but there is a certain amount 

 of likelihood that the two things should be effected in the 

 first instance by the same agency. The fact that the arousing 

 to activity of the central nervous system of a hibernating animal 

 makes it not only begin to shiver (17) or become very active 

 so as to produce heat, but at the same time (or even previously) 

 quickens the heart-beat very considerably (see 6a), also suggests 

 it. It might perhaps be determined whether it were so or not 

 by seeing whether in the first place the animal managed to 

 hibernate if the action of the vagus on the heart were prevented, 

 e.g. by the administration of atropine ; whether in such case the 

 frequency of beat was reduced to the same extent, and if so, 

 secondly, whether under a continuation of the treatment heart- 

 acceleration occurred, and occurred as promptly, on awakening 

 from hibernation. If in spite of such procedure the animal when 

 awake still succeeded in regulating its temperature, we should 

 know that other agencies than the central nervous system were 

 more intimately concerned in adapting the heart to meet the 

 demands made upon it. We should then be in a better position 

 than we are now to discuss whether the power which we have 

 shown to be exercised by the heart in the different species of 

 warm-blooded animals of complying with the demands made 



