THE ENERGY OF THE BODY. 499 



speedily becomes cold ; but for some short time immediately following upon 

 systemic death, a rise of temperature may be observed, due to the fact that, 

 while the metabolism of the tissue is still going on, the loss of heat is some- 

 what checked by the cessation of the circulation. The onset of pronounced 

 rigor mortis causes a marked accession of heat, and when occurring after 

 certain diseases may give rise to a very considerable elevation of tempera- 

 ture. 



This mean bodily temperature of warm-blooded animals is, during health, 

 maintained, with slight variations of which we shall presently speak, within 

 a very narrow margin, a rise, or indeed a fall of much more than a degree 

 #bove or below the limit given above being indicative of some failure in the 

 organism, or of some unusual influence being at work. It is evident, there- 

 fore, that the mechanisms which coordinate the loss with the production of 

 heat must be exceedingly sensitive. It is obvious, moreover, that the mech- 

 anisms may act when the bodily temperature is tending to rise, by either, 

 checking the production or by augmenting the loss of heat ; conversely when 

 the bodily temperature is tending to fall, they may act by either increasing 

 the production or by diminishing the loss of heat. As the regulation of tem- 

 perature by variations in the loss of heat is better known than regulation by 

 variations in production, it will be best to consider the former first. 



446. Regulation by variations in loss. Heat is lost to the body by the 

 warming of the feces and of the urine, by the warming of the expired air, by 

 the evaporation of the water of respiration, by conduction and radiation 

 from the skin, and by the evaporation of the water of perspiration. It has 

 been calculated that the relative amounts of the loss by these several chan- 

 nels are as follows : In warming the feces and urine about 3, or, according 

 to others, 6 per cent. By respiration about 20, or, according to others, 

 about only 9 per cent., leaving 77, or alternately 85, per cent, for conduction 

 and radiation and evaporation by the skin. 



The two chief means of loss, then, which are at all susceptible of any 

 great amount of variation, and which can be used to regulate the tempera- 

 ture of the body, are the skin and the lungs. 



The more air passes in and out of the lungs in a given time, the greater 

 will be the loss in warming the expired air, and in evaporating the water of 

 respiration. In such animals as the dog, which do not perspire freely by the 

 skin, respiration is a most important means of regulating the temperature ; 

 and in the dog a very close connection may be observed between the produc- 

 tion of heat and respiratory activity. The changes which give rise to this 

 loss take place before the inspired air reaches the pulmonary alveoli ; both 

 the warming and the evaporation are effected in the nasal and pharyngeal, 

 and to some extent in the bronchial passages. Some observers have main- 

 tained that the left side of the heart is warmer than the right, and hence 

 have argued that chemical changes leading to a considerable development of 

 heat take place in the pulmonary capillaries. It would appear, however, 

 that the right ventricle, owing to its lying nearer to the liver, the high tem- 

 perature of which has already been mentioned, is, in reality, rather hotter 

 than the left. And, indeed, we have no satisfactory evidence of any large 

 amount of heat being produced by any pulmonary metabolism. 



The great regulator, however, is undoubtedly the skin ; and this has a 

 more or less double action. In the first place, it regulates the loss of heat 

 by means of the vasomotor mechanism. The more blood passes through 

 the skin the greater will be the loss of heat by conduction, radiation, and 

 evaporation. Hence any action of the vasomotor mechanism which, by 

 causing dilatation of the cutaneous vascular areas, leads to a large flow 

 of blood through the skin, will tend to cool the body ; and, conversely, any 



