MAINTENANCE OF THE BODY TEMPERATURE 371 



else. We have saved ourselves to a great extent from 

 the need of such an increase by adapting our clothing to 

 the weather. Animals do the same thing by posture. 

 On a hot summer day a cat may be found stretched at 

 full length with the tail extended and the paws well 

 apart. In this position the fur along the ventral surface 

 is opened to the air. 



On a cold day the cat squats with its paws pressed 

 against the body, the tail laid alongside, and the ventral 

 aspect covered in from the air. The surface exposure 

 cannot be one-half of what it is in the extended attitude. 

 Rabbits generally keep the squatting position and its 

 value is shown by the fact that they readily succumb to 

 cold when they are prevented from doing so. This is 

 the more striking because rabbits endure the most severe 

 climates. 



Temperature Regulation during Exercise. We have 

 considered thus far the problem of temperature main- 

 tenance with varying outward conditions. We have 

 found that within wide limits this is a matter of restrict- 

 ing or facilitating the loss of heat from the body rather 

 than a regulation of the rate of heat production. When 

 a man who has been resting rises and sets out on a brisk 

 walk we have a distinct case to analyze. External 

 factors may be unchanged but the metabolism is much 

 increased. If the body is to be successful in avoiding a 

 fever it must make adjustments to dissipate the extra 

 Calories which it is generating. 



Two factors are recognized which are operative both in 

 the adaptation to warm surroundings and to muscular 

 activity. These are the dilation of the cutaneous vessels 

 and the secretion of sweat. But we must note a differ- 

 ence between the skin which is flushed by contact with 

 warm air and that which glows with exercise. In the 

 former the blood is not moving at an unusual rate 

 through the dilated vessels; in the latter the velocity is 

 presumably increased somewhat with the general quick- 

 ening of the circulation. 



