In Table I is shown data regarding the constitution of different proteins as revealed by another method of analysis known as the Hausmann method. There is in every protein a complex which, when boiled for a few hours with moderately strong mineral acids, yields ammonia. In the table the per cent of the total nitrogen of the protein which is convertible into ammonia is tabulated in the first column under NH3-N. There are three diamino-acids derived from proteins, which are sharply differentiated from all the others by their basic character, that is, they have an alkaline reaction when in solution. They can be precipitated together by means of phos-photungstic acid, and thus separated sharply from all the other constituents of the protein molecule. The remaining amino-acids formed on hydrolysis or digestion of proteins are collectively designated as mono-amino acids. The yields of these are tabulated in the third column. When proteins are heated with acids as is necessary in the method of analysis under discussion, there is always formed a certain amount of black, insoluble nitrogenous substance called humin. It has been shown that most of this comes from the decomposition of a single compound called tryptophan, one of the mono-amino acids. Some proteins are entirely lacking in tryptophan. An example of such a protein is zein of the maize kernel. In the column headed "Total N," is given the per cent of nitrogen in the samples of the proteins employed in the analyses.

Table I. Elementary Composition And Molecular Weights Of Proteins.*

* Osborne, T. B. Zeit. f. analyt. Chem., xli, 25, 1902.

An inspection of this table shows that the amount of nitrogen in the protein molecule which is convertible into ammonia under the conditions of the analysis, varies from as low as 6.46 per cent in legumelin of the pea or bean to as high as 23.78 per cent in gliadin of wheat. In contrast with the proteins of animal origin, it will be noticed that many of the proteins of vegetable origin contain two or three times and a few more than four times the amount of nitrogen in this special ammonia-yielding complex. This is one of the types of data which, as early as 1905, clearly showed that the proteins differ to a great extent in their constitution, and that food proteins are in most cases quite unlike the proteins which compose the muscles and organs of the body.

The method of analysis by means of which the data in Table II were secured, is not a very searching one, and fails to yield as detailed information as is desired for physiological reasoning. For this purpose the differences in the yields of the diamino-acids (bases) in different proteins do not, except in a few instances, contrast markedly with each other. In the case of glutenin, gliadin, hordein and zein, the principal proteins of the wheat, barley, and maize kernels, the content of the basic amino-acids falls far below that present in any of the animal proteins. As will be seen from the next table to be considered, there is more to be learned about this fraction of the protein molecule than the above data reveal. There are three substances in this group, the names of which are arginin, histidin and lysin. Different proteins show marked variation in the content of one or another of them.