These are seeds belonging to a class of plants known as legumes, which are able to utilize the nitrogen of the air for the purpose of synthesizing proteins during growth. Other plants have to secure their nitrogen from the soil in the form of nitrates or ammonium compounds. The legume seeds are much richer in protein than are any of the cereal grains. Wheat, maize, oat, and rice kernels contain about 11, 10, 15 and 9 per cent of protein, respectively, whereas peas and beans contain about 23 per cent. For this reason the latter seeds have long been regarded as especially valuable from the standpoint of protein content. Beans have been frequently spoken of as the "poor man's meat." Unfortunately modern experimental studies have not lent support to this view. Their proteins appear from the results of chemical analysis, to be much more adequately constituted than are those of wheat or maize, but nutrition experiments on animals show clearly that there is something lacking in their molecules which limits the extent to which they can be converted in the body into tissue proteins. The nature of the limiting factor has not been determined (13).