ANIMAL HEAT 373 



strated. An oxidase effects oxidation in the presence of oxygen ; 

 enzymes which only act in the presence of hydrogen peroxide are 

 called peroxidases. It is considered probable that the splitting up 

 of food-stuffs by ordinary hydrolytic ferments is the first stage 

 in the process, and this is followed by the action of oxidases on 

 the split products. To the oxidases is due the formation of 

 carbon dioxide, water, etc., and the production of heat ; the heat 

 formed in the body by the oxidation of fat and carbohydrate 

 is probably the same in amount as is formed in their com- 

 bustion outside ; the nitrogenous moiety of the protein, how- 

 ever, is not fully oxidised, inasmuch as urea and other waste 

 products carry away with them at least one-third of the available 

 energy (p. 365) . How the heat formed in the body is distributed, 

 maintained and lost, must now be considered. 



The Body Temperature. — One important division of the animal 

 kingdom is into warm-blooded and cold-blooded animals. A 

 poikilothermal, cold-blooded, or animal of changeable temperature 

 is one in which the body temperature depends upon its external 

 surroundings. When these are cold the bodies of such animals 

 are cold, being about a degree or so higher than the medium in 

 which they are living. Such a condition exists in reptiles, 

 fish, etc. A homoiothermal, warm-blooded, or animal of practi- 

 cally constant temperature, is one in which the body temperature 

 is independent within wide limits of the temperature of the 

 medium in which it is living : whether this be high or low makes 

 practically no difference. Between these two come a class par- 

 taking of the characters of each, hibernating animals which 

 during the summer are homoiothermal, and during the long 

 winter sleep are poikilothermal. 



The temperature of the body is not uniform, the interior 

 is warmer than the exterior, and the blood in the interior veins 

 is warmer than that in the corresponding arteries. The blood 

 in the veins leading from a gland in a state of activity has a 

 higher temperature than the blood which enters the gland. In 

 the animal body the hottest blood is found in the hepatic veins, 

 while the blood in the posterior vena cava is hotter than that 

 in the anterior. There is also a difference in the temperature 

 of the blood in the right and left hearts ; it is generally considered 

 that the blood in the right heart is the warmest, though Colin 

 found that in the horse the blood of the left side was generally 

 the hottest. The brain has also a high temperature. The 

 practical aspect of the question is that the interior of the body 

 is hotter than the exterior. A surface temperature does not 

 indicate the temperature of the body, which for clinical pur- 

 poses should be taken in the rectum. With the air at freezing- 

 point there may be as much as 3*0° C. (5-4° F.) difference 



