186 ' BALANCE BETWEEN HEATING AND COOLING. 



v< . the kidneys, for the excess that the skin can not evaporate 



tionofthekid- must be strained off Iby these organs. In this regard the 



kidneys act, therefore, vicariously for the skin ; and in hot 

 weather, when the cutaneous losses are great, but little urine is discharged ; 

 but in cold weather, when the cutaneous loss is diminished, the quantity 

 of the urine is increased. 



I think, however, that as regards the respiratory organs, a distinction 



should be made in their mode of action. In reality, they 



Evaporation in J ' > 



the air pas- operate in a double way. 1st. They act, so far as the nasal 

 passages, the trachea, and larger ramifications of the bron- 

 chial tubes are concerned, meteorologically, and therefore variably, for 

 the introduced air possesses the existing atmospheric temperature ; is at 

 one time warm, and at another cold ; yet, since it always leaves these 

 passages at 94, it removes from their surfaces sometimes less and some- 

 times more heat ; but it is not so with the action going on in the air- 

 cells, the temperature of which, and of the air they contain, is always 

 uniform ; and as water vaporizes into them, it must always do it at a uni- 

 form rate, and remove as its caloric of elasticity a uniform amount of 

 heat. I therefore decompose the loss of heat by the respiratory organs 

 into two portions : one, which is constant, and taking place in the cells ; 

 the other, variable, occurring in the large air-ways, and, being meteoro- 

 logical, coincides in this respect with the cutaneous loss. In consider- 

 ing the diseases of the respiratory organs, it is well to keep this distinc- 

 tion in mind. 



The establishment of the equilibrium of temperature in an animal is 

 Balance be- effected* by the mutual operation of the heating and cooling 

 ingandkooMng arr angements. More or less heat, as the system requires, 

 arrangements, may be furnished by promoting or retarding the oxidation 

 of respiratory material ; and since a living being, like an inorganic mass, 

 is subject to every external influence, its temperature tending to rise or 

 fall as diurnal, or annual, or seasonal changes may be, these, as well as 

 Elimination of its own interior variations, are held in check by the cooling 

 local variations or wa rming powers it can exert. Local differences within 

 tion of the itself are eliminated in an indirect, but still very effectual 

 blood. manner, by the circulation of the blood ; and, considering 



the range of variation to which it is exposed, and the frequency of the 

 changes, the required equilibrium is admirably secured. 



I have reserved for a more special and prominent consideration the in- 

 Controi of the fl uence which the nervous system exerts over animal heat, 

 nervous sys- since it is upon this that many have been disposed to deny 

 the great truth that the heat of the body arises from oxida- 

 tion. They say that it is produced by the nerves. Even a mental emo- 

 tion gives rise to disturbance of temperature, and the face may be cover- 



