6 FOOD STUFFS. 



Eggs. Eggs contain about 73 per cent, of water, 15 of 

 albumin, and 12 of fat. Yolk of egg yields lecithin (see 

 " Nervous Tissue ") in considerable quantity, and vitellin, 

 a proteid body analogous to paraglobulin (see "Blood"). 



' Vitellin is obtained when yolk of egg, which has been previously extracted 

 with ether, is treated with solution of common salt. It is precipitated on the 

 addition of water. 



Cereals, Pulses and other Vegetable Foods. Wheat flour 

 derives its alimentary value from its large percentage of 

 proteids (13 per cent.) and starch (73 per cent), but chiefly 

 from its containing gluten, and its consequent adaptedness 

 for bread-making. In the fermentation of dough, grape- 

 sugar splits into alcohol and carbonic acid under the 

 influence of the yeast-plant. By this means the dough is 

 raised. In baking, the dough is subjected to a very high 

 temperature (i 50 C. to 200 C.). Most of the starch becomes 

 soluble, and much of it is converted, especially in the crust, 

 into dextrin. Notwithstanding the destruction of sugar 

 in fermentation, a loaf weighs about a quarter more than 

 the flour used to make it. Rye flour, nearly as rich in 

 proteids and starch as wheat, is also used for bread-making, 

 but yields a less perfect product. It contains more cellu- 

 lose and less albuminous substances. Barley and Oatmeal 

 cannot be so used, as they yield no gluten. They also 

 contain less proteids (5 to 10 per cent.) Barley owes its 

 importance to its being a source of diastase and grape- 

 sugar. Maize, although poor in albuminous bodies, is rich 

 in starch, but in both these respects it is exceeded by rice. 

 Rye and maize are severally liable to a parasitic disease 

 which renders the grain morbific. The Pulses owe their 

 value to the legumin they contain, and to their large per- 

 centage of proteid (23 to 25 per cent.) Potato contains 

 75 per cent, of water. In the dry state it contains about 

 8 per cent, of proteid and 70 per cent, of starch. Its 

 cellulose becomes gelatinous by boiling, and is thus soluble 



