234 Human Physiology. 



natural life of man which may not be properly treated by a 

 scientific and conscientious writer, who seeks only the highest 

 good of his readers. Leaving, then, the whole subject of sex, 

 generation, and hereditary influences to a Part specially and 

 entirely devoted to matters of such profound interest and im- 

 portance, I close this Part with some words on Vital Heat, and 

 Death. 



Heat is the accompaniment of life some hold that heat is 

 life. Plants and trees, while they live, are never so cold as the- 

 wintry air around them. All animals, even those called cold- 

 blooded, resist in some degree changes of temperature. They 

 are never so hot or so cold as the extremes of temperature to 

 which they may be exposed. Man has probably the maximum 

 of this vital power of maintaining an independent temperature. 

 A dead body freezes as soon as the mercury falls below the 

 freezing point, and roasts when exposed to a hot fire. A living, 

 body resists heat and frost. In the polar regions and the tropics 

 the blood remains at the same temperature. Whatever the 

 condition of the skin or the extremities may be, the blood in 

 the centre of the system keeps very nearly at the same degree 

 of warmth, about 98 Fahrenheit. If there is any difference, 

 it is warmer in winter than in summer, because respiration, 

 circulation, and all vital processes are more active. Low 

 animal organisms may be frozen to a certain degree, and still 

 retain life; but in such cases there must be a centre of com- 

 parative warmth and vitality. 



A man can remain in an oven while a beefsteak flesh like 

 his own flesh is thoroughly cooked by his side. Many persons 

 have endured an atmosphere heated to 400 or 500. In the 

 Turkish bath we can bear a temperature of 150 to 200, not 

 only without injury, but often with great comfort and advan- 

 tage. I have taken my morning bath with the thermometer at 

 20 below zero, or in 52 of frost, where every drop of water 

 that fell upon the floor turned instantly to ice, without the least 



