CHAPTER XIV 



ANIMAL HEAT AND ITS REGULATION 



1. THE TEMPERATURE OF THE HUMAN BODY 



BIRDS and Mammals differ from all other living creatures in that their 

 body temperature remains constant in spite of all variations in the tempera- 

 ture of the surrounding medium. For this reason they are called homoiother- 

 mous, or, since the temperature of the medium in which they live is generally 

 lower than their body temperature, warm-flooded animals. 



Among different species of warm-blooded animals the body temperature 

 exhibits considerable differences. In general it is higher in birds (39.4-43.9 

 C.) than in mammals (35.5-40.5 C.), and among the latter many genera 

 have a higher temperature than that of man, 37.5 C. With a temperature 

 as high as the normal in birds, or even as high as the normal in some other 

 mammals, a man would be very ill. 



The temperature of an animal is usually taken in the rectum, that of 

 man either in the rectum or in the mouth or in the axilla. It is evident that 

 the thermometer must always remain in place for a certain length of time 

 if it is to register the temperature exactly; also that the temperature cannot 

 be the same in these different places owing to loss of heat from the superficial 

 parts of the body; and further that of the places named the temperature is 

 highest in the rectum, lowest in the axilla. If the person is doing physical 

 work the temperature in the mouth may fall, whereas the temperature in 

 the rectum rises. This circumstance, which shows that the registration of 

 temperature in the mouth does not always give trustworthy results, is prob- 

 ably due to the cooling of the skin of the face through the agency of sweat, 

 to the augmented respiration by which the lining of the mouth is cooled, etc. 

 (Pembrey and Nicol). 



In taking the rectal temperature it is necessary that the thermometer be 

 inserted to a sufficient depth to register the actual temperature of the interior 

 of the body. In the mouth the thermometer bulb is placed under the tongue 

 and the mouth is closed. The posterior opening of the mouth cavity (see page 

 279) normally is always closed. The axilla never forms a completely closed 

 cavity, but for the purpose* of taking the temperature, can be approximately 

 closed by pressing the arm firmly against the chest wall. It requires, however, 

 some time for the temperature in such a cavity to reach its maximum, and 

 hence the thermometer must remain longer in the axilla than in the mouth or 

 in the rectum. 



The temperature of the surface, especially of the parts habitually exposed, 

 varies greatly, but for the clothed parts can be estimated in general at 



