1893. ANIMAL TEMPERATURE. 217 



these animals find their energy so reduced that they pass the time in 

 sleep — they hibernate. 



The higher animals have been classed as the warm-blooded, the 

 lower as the cold-blooded. This classification is, however, not 

 absolutely exact. Indeed mammals are found, such as the hedgehog, 

 bear, and dormouse, which are in an intermediate position, since, in 

 spite of their high temperature in warm weather, their temperature 

 falls in winter, they become inactive and hibernate, the oxidation of 

 their tissues is reduced to a minimum ; on the other side, there are 

 bees, animals of a low order, which have and maintain a higher 

 temperature than most cold-blooded animals, and are not reduced to 

 spend the winter in slumber. 



In order that an animal may have under very varying conditions 

 a constant temperature, it must possess some regulating mechanism. 

 There are two means by which regulation can be obtained, variation 

 in the amount of heat produced and variation in the loss of heat. 

 Both methods are found in use. When a white mouse, for example, 

 is removed from cold to warm surroundings, it regulates its tempera- 

 ture by increasing the loss of heat from its body, it sweats and 

 exposes to the air as large a surface of its flushed skin as possible ; at 

 the same time, its heat-production is lessened, it is less active, it gives 

 off less carbonic acid, there is less oxidation in its tissues. Let the 

 same animal be now returned to a cold chamber. At once its ears 

 and face become pale, showing that the vessels of the skin contract, 

 and prevent loss of heat by the blood passing to the skin ; when not 

 in active movement the animal huddles up together, ruffles its fur, 

 and makes it as bad a conductor of heat as possible ; it also regulates 

 the heat production, as shown by involuntary shivers or active volun- 

 tary movements, it gives off more carbonic acid, there is increased 

 oxidation in its tissues. 



These regulating mechanisms appear to be under the control of 

 certain parts of the nervous system. The exact anatomical seat is 

 unknown, nor are known the anatomical differences which separate the 

 cold-blooded from the warm-blooded animal, and which would explain 

 the condition of the intermediate forms, such as the hedgehog, the 

 dormouse, bees. It has been shown that by the action of certain 

 nervous poisons, and by intense cold, warm-blooded animals may be 

 made to pass into a condition somewhat resembling that of the cold- 

 blooded animals. Ignorance now reigns here, but not so absolutely 

 for ever. 



M. S. Pembrey. 



