84 



ANATOMY. 



Thus the non-azotized substances, fat, sugar, arid the animal organic 

 acids, are ternary compounds, each consisting of certain quantities of 

 carbon, hydrogen, and oxygen, combined in definite proportions. The 

 percentage composition of some of these substances is stated above. 

 The small figures attached to the letters between the brackets, show 

 the numbers of so-called atoms of each element, which are supposed 

 to enter into combination to form a particular substance; in other 

 words, they show the theoretical atomic composition of that substance. 

 But the percentage composition, representing in round numbers the 

 quantities by weight of each element in 100 parts of the substance, is 

 also of some interest. 



The great characteristic of fats is, that they are very rich in carbon 

 and hydrogen, in proportion to their oxygen: they are known as solid 

 hydrocarbons. In the sugars the number of atoms of carbon is bal- 

 anced, as it were, by as much hydrogen and oxygen as would form the 

 same number of atoms of water ; hence they are frequently named car- 

 bohydrates^ or carbhydrates. 



The azotized substances of the body have a still more complex 

 chemical constitution. Even the simplest of them are quaternary 

 compounds, containing, besides a large amount of nitrogen or azote, 

 certain proportions of carbon, hydrogen, and oxygen. Some of them 

 are even quinary compounds, containing, in addition, either sulphur, 

 iron, or phosphorus, in some yet unknown state of combination. 

 The percentage composition of these azotized substances, as given in 

 the next page, has been more or less accurately determined ; but the 

 atomic constitution of a few of them only, as indicated by the letters 

 and numbers placed between brackets, is well agreed upon. Except 

 keratin, they are all remarkably prone to putrefaction or spontaneous 

 decomposition. 



Of the azotized substances of the body, it is found, as is shown in 

 the following table, that albumen, fibrin, and casein have almost ex- 

 actly the same chemical composition. Each of them, moreover, has a 



