In 1912 Osborne and Mendel (37) performed an experiment which they interpreted as demonstrating the processes of maintenance as being of a lower order than those of growth, and that repair of tissue waste can be effected without the amino-acid lysin, whereas this complex is indispensable for growth. There were two confusing factors in this experiment, the "protein-free milk" nitrogen, and the erroneous belief that gliadin contained but very little lysin.

Osborne had carefully determined the amounts of lysin in numerous proteins and had found the content of this substance in gliadin to be 0.15 per cent. This amount is extremely small compared with the yields obtainable from many other proteins, notably those of animal tissues. This is illustrated by the following table (38):

Lysin In Proteins

In the experiment just referred to they restricted young rats to a diet consisting of gliadin 18.0, "protein-free milk" 28.2, starch 20.8, agar-agar 5.0 and lard 28.0 per cent. The animals were able to maintain their weight during periods as long as 500 days, but were unable to grow to any appreciable extent. When lysin, one of the eighteen digestion products of nearly all proteins, was added to the diet to the extent of 3 per cent of the protein content, the animals were capable of normal development.

At the time these experiments were conducted with gliadin it was assumed that this protein contained but 0.16 per cent of lysin. However, Osborne, Van Slyke, Leavenworth and Vino-grad (39) in 1915 made new analyses of gliadin and other proteins, by a more satisfactory method than that which Osborne had earlier employed (40). They found that gliadin contains about 1.21 per cent of lysin, or about seven times what it was assumed to contain at the time when the conclusion was drawn from feeding experiments with this protein, that lysin is not necessary for maintenance without growth. With this knowledge available, and with the fact made evident that the nitrogen of "protein-free milk" in the quantities used in their experiments, amounts to about half the maintenance requirement of a young animal, there is no longer any reason to regard these data as having any bearing on the problem of the possible dissimilarity in the amino-acid requirements for the processes of maintenance as contrasted with those of growth.