278 Biological Chemistry. 



rately known. From this clot, by certain somewhat 

 complex changes, cheese can be produced. 



Flour consists chiefly of carbohydrate in the form of 

 starch, mixed with a certain amount of proteins. If it is 

 kneaded in a stream of running water the starch can be 

 washed away, and a pasty residue is left known as gluten. 

 This contains two principal proteins namely, gliadin, 

 which can be dissolved out with 70 per cent, alcohol, and 

 glutenin, which can be obtained from the residue after 

 separation of the gliadin, by extraction with very weak 

 solutions of caustic alkali, from which it is precipitated on 

 neutralization with an acid. Other cereals also consist of 

 carbohydrates mixed with proteins. The amount of fat in 

 flour and other cereals is generally very small. 



Vegetables possess a very varied composition. Potatoes 

 consist chiefly of carbohydrates (starch and cellulose), with 

 only small amounts of proteins and fats. The legumes 

 (peas, beans, etc.) contain appreciable amounts of proteins 

 together with starch. The chief constituent of green 

 vegetables is cellulose, but they also contain chlorophyll 

 and other products, the nature of which has not yet been 

 fully determined. 



Meat contains chiefly proteins, with interstitial fat and 

 certain soluble nitrogenous substances (" extractives "), such 

 as creatine and other meat bases. Meat also contains 

 nucleo-proteins. 



Eggs consist both of white and yolk. The former is 

 essentially a solution of various proteins, whereas the 

 latter is a mixture of fats and lipoids (lecithin), and a 

 phospho-protein known as vitellin. If the dried yolks are 

 extracted with ether the fats, together with the pigment, 

 are separated, and a colourless residue remains from which 

 the vitellin can be extracted by treatment with 10 per 

 cent, sodium chloride solution. From this solution it is 





