The fibrine and albumen in the animal frame are derived exclusively from vegetables. For although we seem to derive a portion of the supply from animal food, yet the fibrine and albumen thus supplied have been derived in the beginning from the vegetable kingdom. “It is the peculiar property of the plant,” says Dr. Lankester, “to be able, in the minute cells of which it is composed, to convert the carbonic acid and ammonia which it gets from the atmosphere into fibrine and albumen, and by easy chemical processes we can separate these substances from our vegetable food. Wheat, barley, oats, rye, rice, all contain fibrine, and some of them also albumen. Potatoes, cabbage, and asparagus contain albumen. It is a well-ascertained fact that those substances which contain most of these ‘nutritious secretions,’ as they have been called, support life the longest.” They change little during the process of digestion, entering the blood in a pure state, and being directly employed to renew the nervous and muscular matter which has been used up during work, either mental or muscular. Thus the supply of these substances is continually being drawn upon. The carbon, which forms their principal constituent, is converted into carbonic acid; and the nitrogen, which forms about a sixth part of their substance, re-appears in the nitrogen of urea, a substance which forms the principal solid constituent of the matter daily thrown from the system through the action of the kidneys. Thus the amount of urea which daily passes from the body affords a measure of the work done during the day. “This is not,” says Dr. Lankester, “the mere dream of the theorist; it has been practically demonstrated that increased stress upon the nervous system, viz., brain work, emotion, or excitement from disease, increases the quantity of urea and the demand for nitrogenous food. In the same manner the amount of urea is the representative of the amount of muscular work done.”