66 SELECTION AND PREPARATION OF FOODS 



linseed and cottonseed. In this group, there is more than 

 enough hydrogen to form water with the oxygen pres- 

 ent, 1 and because of this excess of hydrogen they are 

 called hydrocarbons. They are much more valuable as 

 heat producers than the carbohydrates. 2 



Proteids. The presence of nitrogen and sulphur 

 characterizes the third class, examples of which are 

 found in the gluten 3 of wheat and other cereals, and in 

 peas, beans and nuts. These nitrogen-containing sub- 

 stances are called proteids. They have a most com- 

 plex chemical structure, which differs according to the 

 source from which the proteid is obtained. 4 



Animal manufactures. The substances which are 

 found in the bodies of animals closely resemble in chem- 

 ical composition those portions of plants which are used 

 by them for foods and may be similarly classified into 

 carbohydrates, hydrocarbons, and proteids. The carbo- 

 hydrates are chiefly represented by milk sugar and by 

 a starch found in the liver called glycogen; the hydro- 

 carbons, by various fats and oils; and the proteids, by 

 flesh, egg albumin and cheese. They differ from the 

 substances found in plants, however, in the much larger 

 proportion of proteids and hydrocarbons and the 

 much smaller proportion of carbohydrates which they 

 contain. 5 



1 Palm oil, CsiHujiOfi. 



2 The hydrogen not already in combination unites with the oxy- 

 gen of the air, as does also the carbon. The result is the pro- 

 duction of much additional heat and energy. 



8 Gluten is the tenacious gum which remains when raw wheat is 

 chewed. 



4 On the average, 100 Ibs. of ordinary dry proteid contain nearly 

 52 Ibs. of carbon, 7 Ibs. of hydrogen, 16 Ibs. of nitrogen, 2 Ibs. of 

 sulphur, 25 Ibs. of oxygen and a certain amount of mineral 

 material. 



5 Glycogen, C 6 HioO 5 ; milk sugar, Ci 2 H 22 On ; fat (stearin), 



CsvHnoOe; egg albumin, Cao^HssQNsaOeeSg. 



