28 Elementary Biology. 



than those of the carbohydrate group. Their general cha- 

 racters are well known. When acted on by an alkali or super- 

 heated steam, 1 they take up water (hydration) and decompose 

 into glycerin and their corresponding fatty acids (dissocia- 

 tion), which unite with the alkalies to form soaps. The chief 

 neutral fats are palmitin, the chief Constituent of palm oil 

 (' railway grease'), olein, the principal component of olive 

 oil, and stearin, of which beef and mutton fat mainly con- 

 sists. 



The fatty acids comprise a series of bodies which occur 

 chiefly in combination with glycerin to form the neutral fats 

 above mentioned, and with alkalies to form soaps. A 

 number of them will call for special mention afterwards ; at 

 present it will be enough to refer to the fatty acids of the 

 neutral fats, i.e. palmitic, stearic, and oleic acids. 



D. Water (H.,O) is the chief mineral constituent of both 

 plants and animals. It often forms a very large proportion by 

 weight of the organism, constituting over 80 per cent, by 

 weight of the kidney, and over 90 per cent, of many succulent 

 plants, e.g. turnip. The well-known 'jelly-fish' of our seas 

 are composed almost entirely of water, a mere film of solid 

 matter being left after desiccation. Some parts of the 

 organism contain very little water, as for example the enamel 

 of the teeth, where it is present in the proportion of only 0*2 

 per cent. 



E. Salts. The chief inorganic salts are the chlorides, 

 phosphates, carbonates, and sulphates of soda, lime, potash, 

 and magnesia. Salts of iron, manganese, and other metals, 

 also occur. These will call for special mention subse- 

 quently. 



F. Transition substances formed in the integration and 

 disintegration of protoplasm. The nature and signifi- 

 cance of these bodies cannot with advantage be treated of 

 before a discussion of the chemical changes taking place 

 in the organism during growth and decay. One or two 



1 I.e. steam treated under pressure to a temperature above 212 F. 



