ANIMAL HEAT 



495 



and at the end of the observation. This difference is equal to the 

 average specific heat of the animal multiplied by its weight and by 

 the fall of temperature. It can be approximately found by multiply- 

 ing the weight (in kilogrammes or grammes) by the fall of rectal 

 temperature (in degrees), since the average specific heat of the body 

 (of a mammal at least) is not very different from that of water, and the 

 specific heat of water is taken as unity. 



All the higher animals (mammals and birds) have a prac- 

 tically constant internal temperature (fowl 41 to 44 C., 

 mouse 37 to 38, dog 38 to 39, man 37 in the rectum), but 



FIG. 139. AIR CALORIMETER. 



(/.), cross-section ; (//.), longitudinal section ; A, cavity of calori- 

 meter for animal ; B, copper cylinder corrugated so as to increase 

 the radiating surface ; C, air space enclosed between B ai;d a con- 

 centric copper cylinder F ; C is air-tight, and is connected by the tube 2 with the mano- 

 meter M. The other end of the manometer is connected with an exactly similar 

 calorimeter, in which a hydrogen flame is burnt in the space corresponding to A, or in 

 which the air in A is heated by a coil of wire traversed by an electrical current. The 

 flame or current is regulated so as to keep the coloured petroleum or mercury in the 

 manometer M at the same level in both limbs ; the amount of heat given off to the one 

 calorimeter by the flame or current is then equal to that given off by the animal to the 

 other. D is an external cylinder of copper or tin perforated by holes (6, 7) at intervals. 

 The purpose of it is to prevent draughts from affecting the loss of heat from F ; 4, 5, 

 are tubes through which thermometers can be introduced into C ; I is the terminal ot a 

 spiral tube, which is coiled in the end portion of the air space C. The sections of the 

 coils are indicated by small circles. The other end of the spiral tube is 3 ; through 

 this tube air is sucked out, and so the proper ventilation of the animal is kept up. The 

 object of the spiral arrangement is that the air aspirated out of A may give up its heat 

 to the air in C before passing out. E is a door with double glass walls. 



a few hibernating mammals, such as the marmot, are 

 homoiothermal in summer, poikilothermal during their 

 winter sleep. In the lower forms the body temperature 

 follows closely the temperature of the environment, and 

 is never very much above it (frog 0*5 to 2 above 

 external temperature). Both in a frog and in a pigeon 

 heat is evolved as long as life lasts ; but per unit of weight 

 the amphibian produces far less than the bird, and loses 

 far more readily what it does produce. The temperature 

 of the frog may be 30 in June and 5 in January. The 

 structure of its tissues is unaltered and their vitality un- 



