ON ORGANIC CHEMISTRY. 43 



less incomprehensible than that of a leaf or of a muscle ; the production of 

 vermilion, from the union of sulphur and mercury, is as much an enigma as 

 the production of an eye from the substance of the blood. 



According to Lavoisier, an adult mail takes into his system every year 

 827 lbs. of oxygen, and yet he does not increase in weight. What then be- 

 comes of the enormous quantity of oxygen introduced in the course of a year 

 into the human system ? The carbon and hydrogen of certain parts of the 

 body have entered into combination with the oxygen introduced through the 

 lungs and through the skin, and have been given out in the form of carbonic 

 acid and the vapour of water. At every moment, with every expiration, 

 parts of the body are thus removed, and are emitted into the atmosphere. 



No part of the oxygen inspired is again expired as such. Now it is found 

 that an adult inspires 32^ ounces of oxygen daily ; this will convert the car- 

 bon of 24 lbs. of blood into carbonic acid. He must therefore take as much 

 nutriment as will supply the daily loss. And in fact it is found that he does 

 so ; for the average amount of carbon in the daily food of an adult man, 

 taking moderate exercise, is 14 ounces, which require 37 ounces of oxygen 

 for their conversion into carbonic acid. 



But it is obvious, as the inspired oxygen can be removed only by its con- 

 version into carbonic acid and water, that the amount of food necessary for 

 the support of the animal body must be in direct ratio to the quantity of 

 oxygen taken into the system. Thus a child, in whom the organs of respira- 

 tion are naturally in a state of great activity, requires food more frequently, 

 and in greater proportion to its bulk, than an adult, and is also less patient 

 of hunger. A bird deprived of food dies on the third day ; whilst a serpent, 

 which inspires a mere trace of oxygen, can live without food for three months. 

 The number of respirations is less in a state of rest than in exercise, and the 

 amount of food necessary in both conditions must vary also. 



An excess of food is incompatible with a deficiency in respired oxygen, 

 that is, with deficient exercise ; just as violent exercise (which implies an in- 

 creased supply of food) is incompatible with weak digestive organs. 



The capacity of the chest in an animal is a constant quantity ; we there- 

 fore inspire the same volume of air, either at the pole or at the equator, But 

 the weight of the air, and consequently of the oxygen, varies with the tem- 

 perature. Thus an adult man takes into the system daily 46,000 cubic inches 

 of oxygen, which, if the temperature be 77°, weigh 32-| oz. ; but when the 

 temperature sinks down to the freezing point (32°), it will weigh 35 oz. Thus 

 an adult in our climate in winter may inhale 35 oz. of oxygen ; in Sicily he 

 would inspire only 28^ oz. ; and if in Sweden, 36 oz. It is obvious also, that 

 in an equal number of respirations we consume more oxygen at the level of 

 the sea than on a mountain. The quantity of oxygen inspired, and carbonic 

 acid expired, must therefore vary with the height of the barometer. Hence 

 we expire more carbon in cold weather when the barometer is high, than we 

 do in warm weather ; and we must consume more or less carbon in our food 

 in the same proportion. In our own climate, the difference between summer 

 and winter in the carbon expired and therefore necessary for food, is as much 

 as f 



Even when we consume equal weights of food, an infinitely wise Creator 

 has so adjusted it as to meet the exigencies of climate. Thus the fruit, on 

 which the inhabitants of the south delight to feed, contains only 12 per cent, 

 of carbon; whilst the bacon and train-oil enjoyed by the inhabitants of the 

 arctic regions, contain from 66 to 80 per cent, of the same element. 



Now the mutual action between the elements of food and the oxygen of 

 the air is the source of animal heat. 



