HEAT AND LIFE. 401 



extended analysis has thus resulted in an instructive synthesis, which 

 is one of the most signal acquisitions of the experimental method. 



All animals have a temperature above that of the gaseous or fluid 

 media in which they live ; that is to say, they all possess the faculty 

 of producing heat. "Warm-blooded animals maintain an almost con- 

 stant temperature in all latitudes and all climates. Thus, in polar 

 regions, man, mammals, and birds, mark only one or two degrees less 

 than they do at the tropics. The mean temperature of birds is 41 

 (cent.), and that of mammals 37. Those animals called cold-blooded 

 produce heat also, though in a less degree ; but their temperature fol- 

 lows the variations of that of the surrounding medium, keeping, how- 

 ever, a temperature a few degrees higher than it. In reptiles, this 

 excess varies from 5 to half a degree ; in fish and insects, it is still 

 smaller ; and, in the wholly inferior species, it rarely reaches half a 

 degree. In fine, with animals that vary in temperature, the power 

 of resistance to external causes of refrigeration increases in proportion 

 to the perfection of the organization. It is observed, too, that in these- 

 beings vital activity and the force of respiration have a direct relation, 

 to the thermometric state ; thus, in a medium of 7, lizards consume 

 eight times less oxygen than at 23. With animals of constant tem- 

 perature, the reverse is the case ; the colder it is, the more active is 

 their respiration : a man, for instance, who, in summer, consumes only 

 a fraction over an ounce of oxygen an hour, in winter consumes, more 

 than an ounce and a half. Apart from the state of the surrounding 

 medium, many different circumstances exert a perceptible influence 

 on animal heat, and produce tolerably regular variations in it. The 

 seasons, the times of day, sleep, digestion, mode of nourishment, age, 

 etc., are thus constant modifiers of intensity of combustion/ in breath- 

 ing ; but there are such order and harmony, such foresight, one may 

 say, in the organization of the system, that its temperature continues 

 definitively nearly the same in the physiological state. 



The temperature of the human body, at the root of the tongue or 

 under the armpit, is about 37 (cent.) ; this figure expresses the mean 

 found in taking the temperatures of different points of tbe body, for 

 there are certain slight variations in this respect in passing from one 

 organ to another. The skin is the coolest part ; and the more so the 

 nearer we come to the extremities. The temperature rises, on the 

 contrary, with increasing depth of penetration into tbe organism; 

 cavities are much warmer than surfaces. The brain is- cooler than the 

 viscera of the trunk, and the cellular tissue cooler than the muscles. 

 Nor does the blood have the same temperature in. all parts of the 

 body. The labors of Davy and Becquerel established the fact that 

 the blood is warmer the nearer to the heart examinations are made. 

 Claude Bernard measured, by methods of equal ingenuity and exact- 

 vol. 11. 26 



