In the usual method for determining the proteins of a food by multiplying the total nitrogen present by a factor, there is included in the calculation nitrogen that does not come from true proteins, but from compounds that possess physical and chemical properties greatly removed from those which characterize albumin and other true proteins. Their office as nutrients is also less comprehensive than that of the proteins.

63. Amides

Certain non-proteins which are spoken of under the term amides are found chiefly in plants. As-paragine, first found in young asparagus shoots, and glutamine, found in germinating pumpkin seeds, are amides. They are soluble in water, and consequently are diffusible throughout the plant tissues. It is believed that they are the forms in which the nitrogen compounds of the plant are transferred from one part to another, as, for instance, from the stem to the seed. It has generally been held that these bodies are more abundant in young plants than in mature. A larger part of the nitrogen of roots and tubers is found in these compounds than in other foods, the proportion in grains being the least, and is very small indeed. Such investigations as have been conducted point to the conclusion that amides are not muscle-formers, as is the case with proteins. This is a reason for regarding the protein of certain vegetable foods as of less value than that of the grains and grain products.

64. Extractives

These are bodies found in the extract obtained from beef with cold water. After the albumin has been removed from such an extract by boiling, these compounds, known as creatin and creatinih, chiefly constitute the nitrogenous solids that remain. The food value is small, if anything, for they appear to be eliminated from the body in the urine without change.