Kidney, liver and milk proteins stand out as a group of foods containing proteins of unusual value. Among the cereal grains, wheat easily stands first in the quality of its proteins. There is little reason to attempt to place rye, maize, barley, flaxseed oil meal, rolled oats and kaffir corn in their order of values as the sole source of nitrogen in the diet. All that can safely be said is that barley and rye appear to be slightly better than the other seeds named.

Chart 4. - In this chart are shown a series of growth curves of rats which were fed on diets which were comparable in every respect except in the quality of their proteins. All the diets contained 9 per cent of protein except Lot 229, which contained but 8 per cent. It will be seen that rye and flaxseed oil meal furnish a combination of proteins of extraordinary nutritive value, for growth was rapid and the ultimate size attained was great. When the remaining curves are compared it will be seen that 9 per cent of wheat protein produced growth a little less satisfactory than did 8 per cent of milk proteins. None of the other proteins were as good as those mentioned. The steepness of the curve denotes the excellence of the proteins.

Kidney proteins alone, when fed at 9 per cent of the food mixture, appear to give excellent nutrition, and the fact that it is not entirely adequate appears only in the falling off of the fertility of the animals to decidedly below the maximum. As is the rule with families of rats confined through several generations to a monotonous diet, which is faulty in a slight degree, each succeeding generation is smaller when its growth is completed, and in a few generations, indeed, the strain dies out.