PHYSIOLOGICAL CHEMISTRY 363 



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

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

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

 sugar (0'5 %), fatty substances, and inorganic salts. About 85 % of the 

 white is water. We have already studied this. (See Proteins.) The 

 yolk contains about 51 % of water, the solids being mainly fats (31 -75 %), 

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

 about 16 % of protein, and this is mainly of the nature of a phospho- 

 protein called vitellin. The proteins and fats are intimately united 

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

 pounds not being clearly understood. 



The yolk contains about 1 % of inorganic salts, and it is important 

 to note that the phosphorus exists mainly in oi'ganic combination (partly as 

 lecithin and partly as phospho-protein). The same is true of the iron, 

 which also exists in organic combination. Both these inorganic bodies 

 are much more easily assimilated when presented to the tissues in 

 organic combination. 



Meat. As meat consists mainly of the muscle of certain animals, we 

 have already studied its composition in the previous chapter. It con- 

 tains beside muscle a small amount of connective tissue and of fat. 

 (See Table, p. 366.) Much of this fat is not visible to the naked eye, 

 being situated between the muscle fibres. The amount of this fat 

 varies in different animals, and in the same animals constitutes one of 

 the chief differences between "prime" and "inferior" meat. Owing 

 to the large amount of assimilable protein, meat forms one of our 

 chief sources of nitrogen. 



EXPERIMENT I. Cut very finely the piece of meat provided; 

 grind with saline. Filter, and test the filtrate for proteins and salts. 



The Vegetable Food-Stuffs. The most important groups of these 

 are the pulses and the cereals. 



Pulses. The pulses include such bodies as peas, lentils, beans. They 

 contain relatively little water, and are rich in proteins, carbohydrates, 

 and salts. (See Table, p. 366.) They are therefore a very valuable 

 form of foodstuff, more particularly so owing to their cheapness; 

 although it must be remembered that they are not so easily digested as 

 meat, and more is found undigested in the faeces. 



EXPERIMENT II. Extract some of the pea-meal provided with 

 saline. Note the precipitate of globulin on adding a drop to water. 

 Perform the general protein tests. Also extract some with cold water. 

 On heating, a coagulum is obtained showing albumin. Filter. Test 

 filtrate for salts. 



Cereals. These are obtained from the seeds of various artificially 



