FOODS AND THEIR PHYSIOLOGICAL, VALUE. 313 



1. The Proteids. The proteids, or albumens, are foods 

 characterized by containing nitrogen in composition. For 

 this reason they are frequently spoken of as the nitrogenous 

 foods. In addition to the nitrogen they contain carbon, 

 oxygen, hydrogen, and traces of other elements. The pro- 

 teids are familiar in the form of egg albumen, myosin or 

 the lean of meat, casein, the substance of cheese, gluten, 

 the main ingredient of the grains or cereals, and legumen, a 

 vegetable albumen found in relatively great proportion in 

 peas and beans. All the albumens of our diet probably fall 

 into one or the other of these classes. Meats of different 

 sources are physiologically alike and differ only in the mat- 

 ter of flavor and digestibility ; hence all forms of meat would 

 be included under the term "myosin." 



These foods are the main and substantial foods, and 

 have always been recognized as the essential foods, with- 

 out one or more of which it would be impossible to live. 

 Evidently one purpose of foods is to make new tissues; but 

 the tissues, in fact protoplasm wherever found, contains 

 nitrogenous substances closely allied to proteids and albu- 

 mens, and so it is absolutely necessary that to produce 

 these in the body, nitrogenous foods must be taken. In 

 the carbohydrates and hydrocarbons there is no nitrogen, 

 and consequently if our diet should consist wholly of these 

 the tissues of the body would gradually waste away and a 

 death by starvation would ensue. But these proteids or al- 

 bumens do not figure as tissue builders only in the body. 

 They are an integral source of energy. Without trying to 

 press an analogy, it may be helpful to recall that many sub- 

 stances having nitrogen in combination are peculiarly well 

 fitted as sources of energy. One needs only to think of 

 gun-powder with its contained nitre, or of nitro-glycerine 

 with its contained nitrogen, or of a number of other energy- 

 yielding substances which depend for this property largely 

 upon the fact that they have in their composition nitrogen. 

 Disregarding here numerous objections which the chem- 

 ist might urge, it may be said that like these formidable 



