All the leguminous seeds, the ground-nuts, &c., have their nitrogenous constituents displayed under the name of ‘casein.’ The use of this term is rather confusing. In many modern books it does not appear at all in connection with the vegetable kingdom, but is replaced by ‘legumin.’ Liebig regarded this nitrogenous constituent of the leguminous seeds, almonds, &c., as identical with the casein of milk, and it was a pupil and friend of Liebig’s—the late Prince Consort—who devised and originally supervised this graphic method of displaying the chemistry of food.[16] I will not here discuss the vexed question of whether the analyses of Liebig, identifying legumin with casein, or rather those of Dumas and Cahours, who state that the vegetable casein is not of the same composition as animal casein, are correct. The following figures display my justification for thus lightly treating the discussion: +--------------------+--------+---------+---------+---------+ | -- | Casein | Legumin | Legumin | Legumin | +--------------------+--------+---------+---------+---------+ | Carbon | 53·7 | 50·50 | 55·05 | 56·24 | | Hydrogen | 7·2 | 6·78 | 7·59 | 7·97 | | Nitrogen | 16·6 | 18·17 | 15·89 | 15·83 | | Oxygen and Sulphur | 22·5 | 24·55 | 21·47 | 19·96 | +--------------------+--------+---------+---------+---------+ The first column shows the results of Dumas for animal casein; the second, those of Dumas and Cahours for legumin; the third, those of Jones for the same; and the fourth, those of Rochleder; all as quoted by Lehmann. Here it will be seen that the differences upon which Dumas and Cahours base their supposed refutation of the identity of the animal with the vegetable principle are much smaller than the differences between the results of different analyses of the latter. These differences I suspect are all due to the difficulty of isolating the substances in question, especially of the vegetable substance, which is so intimately mixed with the starch, &c., in its natural condition that complete separation is of questionable possibility. The difficulty (or impossibility) of driving off all the adhering water, without removing the combined elements of water, is a further source of discrepancy. This will be understood by the following description of the method of separation as given by Miller (‘Elements of Chemistry,’ vol. iii.). ‘Legumin is usually extracted from peas or from almonds, by digesting the pulp of the crushed seeds in warm water for two or three hours. The undissolved portion is strained off by means of linen, and the turbid liquid allowed to deposit the starch which it holds in suspension; it is then filtered and mixed with dilute acetic acid. A white flocculent precipitate is thus formed, which must be collected on a filter and washed.’