ANIMAL HEAT. 311 



according to the tables of Tiedemann and Rudolph i, averages 101 

 (38.3 C.). The extremes recorded by them were 96 and 106, the former 

 in the narwhal, the latter in a bat ( Vespertilio pipistrella). In Birds, the 

 average is as high as 107 (41 -2 C.); the highest temperature, 111-25 

 (40 -2 C.); being in the small species, the linnets, etc. Among Reptiles, 

 while the medium they were in was 75 (23 '9 C.) their average tempera- 

 ture was 82 -5 (31*2 C.). As a general rule, their temperature, though 

 it falls with that of the surrounding medium, is, -in temperate media, two 

 or more degrees higher; and though it rises also with that of the medium, 

 yet at very high degrees it ceases to do so, and remains even lower than 

 that of the medium. Fish and invertebrata present, as a general rule, the 

 same temperature as the medium in which they live, whether that be high 

 or low; only among fish, the tunny tribe, with strong hearts and red 

 meat-like muscles, and more blood than the average of fish have, are 

 generally 7 (3 '8 C.) warmer than the water around them. 



The difference, therefore, between what are commonly called the warm 

 and the cold-blooded animals, is not one of absolutely higher or lower 

 temperature: for the animals which to us in a temperate climate feel cold 

 (being like the air or water, colder than the surface of our bodies), would 

 in an external temperature of 100 (37 '8 C.) have nearly the same tem- 

 perature and feel hot to us. The real difference is that what we call 

 warm-blooded animals (Birds and Mammalia), have a certain "permanent 

 heat in all atmospheres," while the temperature of the others, which we 

 call cold-blooded, is "variable with every atmosphere." (Hunter.) 



The power of maintaining a uniform temperature, which Mammalia 

 and Birds possess, is combined with the want of power to endure such 

 changes of body temperature as are harmless to the other classes; and 

 when their power of resisting change of temperature ceases, they suffer 

 serious disturbance or die. 



Sources and Mode of Production of Heat in the Body. 



The heat which is produced in the body arises from combustion, and is 

 due to the fact that the oxygen of the atmosphere taken into the system 

 is combined with the carbon and hydrogen of the tissues. Any changes 

 which occur in the protoplasm of the tissues, resulting in an exhibition 

 of their function, is attended by the evolution of heat and also by the pro- 

 duction of carbonic acid and water; and the more active the changes, 

 the greater the heat produced and the greater the amount of the carbonic 

 acid and water formed. But in order that the protoplasm may perform 

 its function, the waste of its own tissue (destructive metabolism), must 

 be repaired by the supply of food material, and therefore for the produc- 

 tion of heat it is necessary to supply food. In the tissues, therefore, 

 two processes are continually going on: the building up of the protoplasm 

 from the food (constructive metabolism), which is not accompanied by 

 the evolution of heat but possibly by the reverse, and the oxidation of the 

 protoplastic materials, resulting in the production of energy, by which 

 heat is produced and carbonic acid and water are evolved. Some heat 

 will also be generated in the combination of sulphur and phosphorus with 

 oxygen, but the amount, thus produced is but small. 



