SECTION II 



THE PROXIMATE CONSTITUENTS OF THE 



ANIMAL BODY 



IN spite of the enormous variety of the proximate constituents of 

 living organisms, they are all members or derivatives of three 

 classes of compounds. Since living organisms form the entire 

 food of the animal kingdom, a study of these proximate con- 

 stituents includes the study of all the food-stuffs. These classes 

 are : 



(a) Proteins, containing the elements carbon, hydrogen, nitrogen, 

 oxygen, and sulphur ; in some cases also phosphorus. 



(b) Fats, containing carbon, hydrogen, and oxygen. 



(c) Carbohydrates, containing carbon, hydrogen, and oxygen, the 

 two latter elements being present in the proportions in which they 

 form water. 



THE CHIEF TYPES OF ORGANIC COMPOUNDS OCCURRING 



IN THE ANIMAL BODY 



Tiie full consideration of the various modifications undergone by these 

 three classes of food-stuffs in the body, especially if we include the by-products 

 occurring both in plants and in animal metabolism, involves a wide knowledge 

 of organic chemistry, which indeed at its origin was simply the chemistry of 

 the products of living (i.e. organised) beings. The most important substances 

 with which we shall have to deal belong to a comparatively restricted number 

 of groups. For the convenience of the reader a short summary of the relation- 

 ships of these groups to one another and to the hydrocarbons is given here. 



THE HYDROCARBONS (FATTY SERIES). These form a continuous homo- 

 logous series, and may be saturated or unsaturated. Examples of the saturated 

 series are : 



CH 4 methane 



C 2 H 6 ethane 



C 3 H 8 propane 



C 4 H 10 butane, and so on, 



the general formula for the group being 



These paraffins, the lower members of which are gaseous, while the higher 

 members form the petroleum ether, the heavy petroleums, vaseline, and the 

 paraffin wax with which we are all familiar, are entirely inert in the animal 

 body. If taken with the food they pass through the alimentary canal un- 

 changed. In order to render them accessible to the action of the living cell 

 they must first undergo oxidation. 



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