78 SCIENCE PROGRESS 



prevent as much loss of heat as possible. I kept a young 

 crocodile for some months in a long trough so arranged that 

 one end but not the other could be heated from outside. It was 

 so heated every night when the weather was cold, but the 

 crocodile was found indifferently in any part of the trough in 

 the morning, until at last one night in a somewhat longer spell 

 of cold weather it died at the very furthest extremity of the 

 trough from the warmed part. It could have been in a sur- 

 rounding temperature of 8° C. had it liked ; it chose one that was 

 hardly above freezing-point and died there. A warm-blooded 

 animal, feeling the cold, would have made every effort both to 

 prevent loss of heat and to produce more heat ; even without 

 effort it would, with the aid of the central nervous system, that 

 is to say reflexly, have done one or other or both things, in 

 some species more the one, in some more the other. 



Is it also by means of the central nervous system that the 

 muscles, put into play either voluntarily or involuntarily to 

 produce the extra amount of heat and taking up more oxygen 

 from the blood, ask the heart to make good the loss ? It is well 

 known that muscular action is accompanied by acceleration of 

 the heart, and that acceleration of the heart may be brought 

 about by the intervention of nerves. But to answer the question 

 we have to know a good deal more than this, and, in the first 

 place, whether either reflexly by the excitation of the afferent 

 nerves from the muscle or by the action of motor cells of the 

 cortex such acceleration can be produced, also whether poikolo- 

 thermic vertebrates differ from homoeothermic ones in this 

 respect. That it can be produced in one or other of these 

 ways in one species of homoeothermic vertebrate, namely man, 

 is shown, I think conclusively, by the results obtained from 

 experiments which, by the kindness of several Oxford under- 

 graduates in serving as subjects for them, I have been able 

 to make. Having recorded the frequency of the beat with the 

 subject sitting quietly with one hand and one foot in basins of 

 salt water connected with the terminals of the capillary electro- 

 meter, it was then again recorded when, instead of being at rest, 

 he clenched the fist that was free, or made some other definite 

 muscular action, on hearing a signal given automatically just as 

 the plate began to pass behind the capillary electrometer, and 

 throwing its shadow on to the plate so that the exact moment at 

 which the sound was made was recorded. The reaction-time of 



