594 A MANUAL OF PHYSIOLOGY 



the air which it is the function of the fur to maintain at rest around it 

 be thus expelled, the animal dies of cold, unless the loss of heat is 

 artificially prevented. If, without varnishing at all, the greater 

 portion of the skin of a rabbit or guinea-pig be closely clipped or 

 shaved, similar phenomena are observed. iPre vented from covering 

 itself with straw, the animal dies, sometimes in twenty-four hours. 

 The radiation from the skin, as measured by the resistance-radio- 

 meter (p. 574), is greatly increased ; the animal shivers constantly, 

 and the rectal temperature falls. Placed in a warm chamber before 

 the temperature in the rectum has fallen below 25, the animal 

 recovers perfectly. If the fall is allowed to go on, it dies. If it 

 is kept from the first in the warm chamber, no fall of temperature 

 occurs. When the increased loss of heat is less perfectly compen- 

 sated when, for example, the animal is left at the ordinary tem- 

 perature, but supplied with sufficient straw to cover itself, or allowed 

 to crouch among other animals a curious phenomenon may some- 

 times be seen. The rectal temperature, which has fallen sharply 

 during the operation, remains subnormal (as much as 2 to 3 below 

 the ordinary temperature) for a time (a week or more), and then 

 gradually rises as the coat again begins to grow. The meaning of 

 this seems to be that the power of regulating the temperature by 

 increasing the metabolism is overtasked by the removal of the 

 natural protective covering, unless the escape of heat is artificially 

 diminished. When the loss of the fur is entirely compensated, no 

 fall of temperature occurs ; when it is not compensated at all, the 

 animal cools till it dies ; when it is partially compensated, the 

 increased metabolism may only suffice to maintain a temperature 

 lower than the normal, although constant muscular contractions 

 (shivering) are brought in to supplement the efforts of the regulative 

 chemical processes. 



Hitherto we have only spoken of a reflex regulation of the 

 heat-production called into play by external cold. It might 

 be supposed and, indeed, has often been assumed that heat 

 would lessen the metabolism, as cold increases it ; and there are 

 indications that in the smaller animals this is the case, although 

 the influence of heat seems to be much smaller than the influence 

 of cold. But neither experimental results nor general reasoning 

 have as yet shown that in man, either in the tropics (Eykman) 

 or in the north temperate zone (Loewy), the chemical tone is 

 diminished by a rise of external temperature much above the 

 mean of an ordinary English summer, apart from the effect of 

 the muscular relaxation which heat induces. In a man, indeed, 

 at rest in a hot atmosphere, the production of carbon dioxide 

 and consumption of oxygen are, if anything, greater than at 

 the ordinary temperature. The regulation of temperature in 

 an environment warmer than the normal seems, in fact, to be 

 brought about more by an increase in the loss than a decrease 

 in the production of heat. Evaporation from the skin and lungs 

 is an automatic check upon overheating as important as the 

 involuntary increase of metabolism upon excessive cooling. 



While it is known that the skeletal muscles, and perhaps the 



