FOOD 285 



Occurrence. — Non- proteins are most abundant in plants 

 where growth is most active, e.g. seedlings. In young 

 plants the amount of nitrogen in these compounds may 

 exceed that in proteins. As the plant reaches maturity the 

 amount of nitros^en in non-protein form decreases. Soluble 

 nitrogen compounds are especially abundant in roots and 

 tubers. In the potato the greater part of tlie nitrogen is in 

 the non-protein form. 



2. Fats and Allied Bodies. 



Nature. — The chemistry (p. 41) and energy value (p. 257) 

 of tlie fats have been already considered. 



In the food they may be substituted for an amount of 

 carbohydrate of equal energy value, i.e. they are isodynamic 

 with the carbohydrates. 



Occurrence. — Fats are more abundant in animals than in 

 plants. The amount present in the animal body varies 

 within very wide limits. In fat oxen and sheep nearly 

 50 per cent, of the weight of the carcase may consist of fat. 



In plants they occur chiefly in oil seeds where they form 

 a concentrated reserve material. Small quantities are 

 present, however, in all parts of plants. 



In addition to true fats there exist in plants fatty acids 

 and various bodies related to fats. These, together with 

 resins and waxes which resemble fats in their physical 

 properties rather than in their chemical composition, can 

 all be extracted with ether, which is the conventional method 

 adopted in quantitative analysis. In dealing with the 

 constituents of feeding-stufts, therefore, it is customary to 

 class all these bodies soluble in ether as " crude fat," or 

 more properly as "ether extract." 



3. Carbohydrates. 



Nature. — Carbohydrates contain carbon, hydrogen, and 

 oxygen, the carbon atoms of the molecule usually number- 

 ing six or some multiple of six, and the hydrogen and 

 oxygen are in the same proportions in which they occur in 

 water. They are aldoses or ketoses (Appendix), and deriva- 

 tives of these, of the hexatomic alcohol, CgHi^Og (Appendix). 



