VARIATIONS IN THE HEAT OF THE BODY. 875 



are placed under favorable conditions of protection. But the power 

 of infants and very young children, as well as of the aged, to resist 

 the lowering effects of cold is less than in the adult. Experiments on 

 the young of Mammalia and Birds, show this ; their small bodies, and 

 also those of the human infant, will cool comparatively more rapidly, 

 by radiation arid conduction, than those of adult animals and Man ; 

 their calorific power may be as great, but they cool more quickly. 

 Hence the greater necessity for the protection of clothing, and for ar- 

 tificial warmth. 



The influence of race is also slight or ineffective. In hot climates, 

 and in hot seasons, the mean temperature of the body is somewhat 

 higher than in cold climates and seasons, the difference being more 

 marked in animals than in Man. The difference, however, usually 

 amounts to not more than from 1 to 2, showing how slight is the 

 influence of climate, and proving the independence of the temperature 

 of warm-blooded creatures of external changes. According to Dr. I. 

 Davy, however, in a long series of observations, whilst the external 

 temperature varied as much as 22 Fahr., i. e., from 60 to 82, that 

 of the body fluctuated 5.5 Fahr., i. e., from 96.5 to 102. The power 

 of Man to resist, and accommodate himself to, climatic variations of 

 temperature, is greatly aided by shelter, clothes, fire, means of cool- 

 ing the air, and peculiar selection of food ; he can create an artificial 

 climate, and protect himself against its hostile influences. Sleep 

 lowers the temperature of the body from 1 to 2, all the organic func- 

 tions, even circulation and respiration, being at that time likewise less 

 active. No constant diurnal variations of the temperature of the body, 

 in Man, have been observed ; but, in Birds, the highest temperature 

 seems to be attained at noon, and the lowest about midnight. (Chossat.) 

 Exercise increases not only the sensation of warmth in the body, but 

 actually raises the average temperature ; the effects, however, being 

 by far most evident in the extremities. Thus, the general tempera- 

 ture after quick running, may become nearly 2 warmer ; after walk- 

 ing, the deep-seated parts show little or no change, whilst the feet and 

 hands are raised many degrees, the action of the heart and lungs 

 being quickened, as well as that of the muscular system generally, so 

 that more rapid metamorphoses take place (pp. 813, 844). Deficient 

 food and positive abstinence, lower the temperature ; why, will be ex- 

 plained hereafter ; on the other hand, abundance of food and the use 

 of stimulants, ultimately increase it; but the immediate effect of a 

 meal, or of taking wine, is said to be temporarily to lower the animal 

 heat. The depression of the temperature, observed in animals in 

 which the skin is covered with an impermeable varnish, has already 

 been mentioned (p. 795). According to Becquerel and Breschet, in 

 rabbits so treated, the temperature falls speedily from 100 to about 

 75, before death takes place. The change in the color of the fur or 

 feathers to white as winter approaches, in the case of Arctic mam- 

 malia and birds, retards radiation, and so conserves their animal heat. 

 In disease, the temperature of the human body has been found to 

 rise or fall many degrees above, or below, the normal temperature. 

 Thus, in fevers with acceleration of the pulse and respiration, in active 



