ELEMENTARY PHYSIOLOGICAL CHEMISTRY 

 This diet yields : 



211 



These facts show us how important it is to know the exact composi- 

 tion of the various food-stuffs, so that we may be in a position to 

 draw up an adequate diet sheet. 



The organic food stuffs may conveniently be divided into two classes, 

 the animal and the vegetable. 



The Animal Food Stuffs. The two most important of these, viz. 

 milk and meat, have been discussed in separate chapters. 



Eggs form another important class of animal foods. 



Eggs. A hen's egg weighs about two ounces or fifty grammes. The 

 shell forms about 12 per cent, of the total weight, and consists mainly 

 of carbonate of lime. The white consists of a multitude of very fine 

 fibrous envelopes filled with a solution of proteid (chiefly egg-albumin, 

 but also traces of egg globulin and egg mucoid), containing traces of 

 sugar (0-5 per cent.), fatty substances, and inorganic salts. About 

 85 per cent, of the white is water. The yolk contains about 51 per 

 cent, of water, the solids being mainly fats (31-75 per cent.), the chief 

 of which is the phosphorised fat lecithin. It also contains about 

 16 per cent, of proteid, and this is mainly of the nature of a nucleo- 

 proteid called vitellin. The proteids and fats are intimately united 

 with one another in the yolk, the exact nature of the resulting 

 compounds being very little understood. 



The yolk contains about 1 per cent, of inorganic salts, and it is 

 important to note that the phosphorus exists mainly in organic combination 

 {partly as lecithin and partly as nuclein). The same is true of the 

 iron, which exists in organic combination with nuclein. Both these 

 inorganic bodies are much more easily assimilated when presented 

 to the tissues in organic combination. 



The Vegetable Food Stuffs. One of the most important groups of 

 these is 



Cereals. These are obtained from the seeds of various artificially 

 cultivated grasses, and they all contain representatives of the various 



