10 



ANIMAL CHEMISTRY. 



creases with the difference between the tern- | 

 perature of the heated body and that of the } 

 surrounding medium ; that is, the colder the | 

 surrounding medium the shorter the time 

 required for the cooling of the heated body. 



How unequal, then, must be the loss of 

 heat in a maa at Palermo, where the exter- 

 nal temperature is nearly equal to that of the 

 body, and in the polar regions, where the 

 external temperature is from 70 to 90 

 lower. 



Yet, notwithstanding this extremely un- 

 equal loss of heat, experience has shown 

 that the blood of the inhabitant of the arctic 

 circle has a temperature as high as that of 

 the native of the south, who lives in so dif- 

 ferent a medium. 



This fact, when its true significance is per- 

 ceived, proves that the heat given off to the 

 surrounding medium is restored within the 

 Body with great rapidity. This compensa- 

 tion takes place more rapidly in winter than 

 in summer, at the pole than at the equator. 



Now, in different climates the quantity of 

 oxygen introduced into the system of respi- 

 ration, as has been already shown, varies 

 according to the temperature of the exter- 

 nal air ; the quantity of inspired oxygen in- 

 creases with the loss of heat by external 

 cooling, and the quantity of carbon or hydro- 

 gen necessary to combine with this oxygen 

 must be increased in the same ratio. 



It is evident that the supply of the heat 

 iost by cooling is effected by the mutual 

 action of the elements of the food and the 

 inspired oxygen, which combine together. 

 To make use of a familiar, but not on that 

 account a less just illustration, the animal 

 body acts, in this respect, as a furnace, 

 which we supply with fuel. It signifies 

 nothing what intermediate forms food may 

 assume, what changes it may undergo in the 

 body, the last change is uniformly the con- 

 version of its carbon into carbonic acid, and 

 qf its hydrogen into water; the unassimila- 

 ted nitrogen of the food, along with the un- 

 burned or unoxidised carbon, is expelled in 

 the urine or in the solid excrements. In 

 order to keep up in the furnace a constant 

 temperature, we must vary the supply of 

 fuel according to the external temperature, 

 that is, according to the supply of oxygen. 



In the animal body the food is the fuel ; 

 with a proper supply of oxygen we obtain 

 the heat given out during its oxidation or 

 combustion. In winter, when we take 

 exercise in a cold atmosphere, and when 

 consequently, the amount of inspired oxygen 

 increases, the necessity for food containing 

 carbon and hydrogen increases in the same 

 ratio; and by gratifying the appetite thus 

 excited, we obtain the most efficient protec- 

 tion against the most piercing cold. A 

 starving man is soon frozen to death ; and 

 every one knows that the animals of prey 

 in the arctic regions far exceed in voracity 

 those of the torrid zone. 



In cold and temperate climates, the air, 

 which incessantly strives to consume the 



body, urges man to labourious eflorts in 

 order to furnish the means of resistance to 

 its action, while, in hot climates, the neces- 

 sity of labour to provide food is far less 

 urgent. 



Our clothing is merely an equivalent for 

 a certain amount of food. The more warmly 

 we are clothed the less urgent becomes the 

 appetite for food, because the loss of heat 

 by cooling, and consequently the amount 

 of heat to be supplied by the food, is di- 

 minished. 



If we were to go naked, like certain savage 

 tribes, or if in hunting or fishing we were 

 exposed to the same degree of cold as the 

 Samoyedes, we should be able with ease to 

 consume 10 Ibs. of flesh, and perhaps, a 

 dozen of tallow candles into the bargain, 

 daily, as warmly clad travellers have re- 

 lated with astonishment of these people! 

 We should, then, also be able to take the 

 same quantity of brandy or train oil without 

 bad effects, because the carbon and hydrogen 

 of these substances would only suffice to 

 keep up the equilibrium between the exter- 

 nal temperature and that of our bodies. 



According to the preceding expositions, 

 the quantity of food is regulated by the 

 number of respirations, by the temperature 

 of the air, and by the amount of heat given 

 off to the surrounding medium. 



No isolated fact, apparently opposed to 

 this statement, can affect the truth of this 

 natural law. Without temporary or perma- 

 nent injury to health, the Neapolitan cannot 

 take more carbon and hydrogen in the shape 

 of food than he expires as carbonic acid 

 and water ; and the Esquimaux cannot ex- 

 pire more carbon and hydrogen than he 

 takes into the system as food, unless in a 

 state of disease or of starvation. Let us ex- 

 amine these states a little more closely. 



The Englishman in Jamaica sees with 

 regret the disappearance of his appetite, 

 previously a source of frequently recurring 

 enjoyment ; and he succeeds by the use of 

 cayenne pepper and the most powerful 

 stimulants, in enabling himself to take as 

 much food as he was accustomed to eat at 

 home. But the whole of the carbon thus 

 introduced into the system is not consumed; 

 the temperature of the air is too high, and 

 the oppressive heat does not allow him to 

 increase the number of respirations by active 

 exercise, and thus to proportion the waste 

 to the amount of food taken; disease of 

 some kind, therefore, ensues. 



On the other hand, England sends her 

 sick, whose diseased digestive organs have 

 in a greater or less degree lost the power of 

 bringing the food into that state in which it 

 is best adapted for oxidation, and therefore, 

 furnish less resistance to the oxidising 

 agency of the atmosphere than is required 

 in their native climate, to southern regions 

 where the amount of inspired oxygen is 

 diminished in so great a proportion; and 

 the result, an improvement in the health, 

 is obvious. The diseased organs of diges- 



