504 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1910, 



involving mechanical movements of the blood is hardly conceivable. 

 The shortening of the cycle in cases of such slight action is due to 

 shortening of the diastole only, and MacWilliam's researches (12) 

 on cats have shown us that it is the vagTis nerve which principally, if 

 not solely, affects the duration of diastole, and that stimulation of 

 the peripheral end of this nerve produces an immediate effect, whereas 

 that of the accelerator nerve to the heart (the sympathetic) takes 

 some few seconds to produce one. We can therefore not only say 

 from the promptitude with which the heart accelerates when a volun- 

 tary action is made that it is due to nerve action, but also that it is 

 the vagus nerve which conveys the impulse to the heart and therefore 

 that the nerve which acts on the vagus center, whether the sensory 

 nerve of a muscle or an axon from a cortex cell, acts in such a way 

 as to suspend the tonic action of the center. Bowen, in a paper (15) 

 discovered after these experiments had been made, has shown that 

 even so small an action as gently tapping a key, the subject being at 

 rest with his arm supported on a table, produces a prompt accelera- 

 tion of the heart. His method of recording does not show so well as 

 that described above how prompt it is, but he saw that it was enough 

 to indicate 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 j)art 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 involuntai^^ refiexly produced, muscular movements for 

 the regulation of temperature such as shivering, evidence of which 

 acceleration I have obtained from one or two medical undergradu- 

 ates who kindly took their pulse rates several times under conditions 

 which induced shivering for comparison with what it Avas before the 

 shivering commenced. Since the shivering can not be made to begin 

 at a precise moment, we can not 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 ner- 

 vous system ; but there is a certain amount of likelihod 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 pre- 

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

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

 by seeing whether in the first place the animal managed to hibernate 



