TRANSAGTIONS OF SECTION I. 791 



Section I.— PHYSIOLOGY. 



Peesident of the Section — Professor E. A. Schafbk, F.R.S. 



THURSDAY, AUGUST 9. 



[The President's Address was delivered on Friday, August 10.— See p. 795.] 

 The following Papers were read : — 



1. The Resiyonse of Animals to Changes of Temperature. 

 By M. S. Pembrey, M.A., M.B. 



The simplest method of investigating the response of animals to changes of 

 temperature is to determine the amounts of carbonic acid which they discharge. 

 The carbonic acid is a measure, it may be not an exact one, of the heat produced. 

 Prom this point of view a series of experiments have been made upon the power 

 which warm-blooded animals possess of varying their production and loss of heat 

 in such a way that their mean temperature is constant. 



A mouse is a very suitable animal for such experiments, because on account of 

 its large cutaneous surface compared with its small bulk the reaction to a change 

 of temperature is very rapid. Within two minutes of a fall in external temperature 

 from 30° to 18° the mouse increases its output of carbonic acid by 74 per cent. ; 

 within one minute of a change from 33°'i!5 to 17°'6 the increase is 60 per cent. 

 The response to a rise in temperature is not so rapid : within two minutes of a rise 

 from 18° to 34°'5 the decrease in carbonic acid is 18 per cent. ; within one minute 

 ■of a change from 17° to 32° the decrease is 5 per cent. With cold surroundmgs the 

 mouse is very active, whereas with a warm temperature it becomes quiet and goes 

 to sleep. The relationship between muscular activity and the production of heat 

 is well shown.' 



Experiments were next made upon the developing chick. It is a warm-blooded 

 animal, but during its development it was probable that it passed through a stage 

 in which it would have responded to changes of temperature in a similar way 

 to that seen in cold-blooded animals ; that in cold surroundings it would have pro- 

 duced less carbonic acid, but that with a rise in temperature it would have increased 

 its output of carbonic acid. The experiments show that during the greater part of 

 the period of incubation the developing chick responds to changes of temperature in 

 a similar manner to that of a cold-blooded animal ; that towards the end of incuba- 

 tion, about the 20th or 21st day, there is an apparently neutral stage in which no 

 marked response is seen ; that this neutral condition is succeeded, when the chick 

 is hatched, by a warm-blooded stage. The intermediate stage may be the resultant 

 of two opposite tendencies — on the one hand the cold-blooded condition, on the 

 other the imperfectly developed power of regulating the production of heat. When 



» ' On the Reaction-time of Mammals to Changes in the Temperature of their 

 Surroundings,' Journal of Physiology, xv. 1893, p. 401. 



