SECTION II 



THE PROXIMATE CONSTITUENTS OF THE 

 ANIMAL BODY 



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 constituents 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. 



(6) 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 



The 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 relationships of these groups to one another and to the 

 hydrocarbons is given here. 



THE HYDROCARBONS (FATTY SERIES). These form a continuous homologous 

 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 



C n H 2n + 2 . 



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 unchanged. In order to render them 

 accessible to the action of the living cell they must first undergo oxidation. 



The unsaturated hydrocarbons have the general formulae C^H^, C n H 2o _ 2 > 

 .4, &c. 



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