It is well, since we are so dependent on foods of this class, that we have two quite distinct sources from which they may be taken. The great bulk comes to us in the form of meats, including poultry, game, oysters and fish of various kinds, in addition to beef, mutton, and hog-meat in its several forms. Of animal origin also we have eggs, which are among the most valuable of all foods of this class on account of their high digestibility.
From the vegetable world we get albumins known as legumins, which differ somewhat from those obtained from animal sources, though taking their place in the economy in all essential particulars. Unfortunately the legumins are usually so mixed with starches and other vegetable substances less digestible, that it is necessary to take a large bulk of foods of this latter class in order to secure anything like the requisite amount of the former.
Before taking up individually the various albuminous foods, the writer would again direct attention to the chapter on cooking, and would strongly urge upon the reader the proper methods of preparing nitrogenous foods therein stated. Where the albumins are in a nearly pure state, as in milk and eggs, they are slightly more digestible when raw, but all meats should be cooked until only the faintest tinge of red remains if we wish to have them prepared in the most wholesome way for those with delicate digestions. Meats are, as a rule, most wholesome when cooked "very done."
It has long been the cry of sentimentalists that no living being should die in order that man might exist. Unfortunately for such theories, the stern and unbending edict of nature has negatived views of this kind ages before the altruistic philosopher came on the scene, and we are daily constrained to bow to this mandate of one of the primal laws of existence. However much we might desire it otherwise, it has been written that "only in death is there life;" nor may any animal being disobey and continue to exist. As has been already explained, the human being cannot thrive on vegetable substances alone; from them he may get a certain amount of nitrogen in the form of legumin, but there is not enough to make up for the waste of this substance that constantly goes on in the body.