The albuminates, or nitrogenous foods, were formerly designated by the older writers on dietetics as flesh-formers, the hydro-carbons, or non-nitrogenous foods, being classified as force-producers: Recent researches have, however, shown that this sharp division of foods into nitrogenous, or flesh-formers, and non-nitrogenous, or force-producers, cannot any longer be maintained. It has been proved by experiment that the muscles do not undergo waste during exercise, which waste has to be restored by nitrogenous food, in anything like the degree which was formerly thought and taught by Liebig. In fact, the amount of tissue waste in muscular exercise is small, and hence the amount of nitrogenous food necessary for repair is also small. The life and health, however, of all the organic nitrogenous tissues, fluids, and secretions can only be maintained by constant change. As the blood circulates through the body, carrying the elements of nutrition to the furthermost limits of the tissues, it modifies all with which it comes in contact; here parting with some element in order to promote cell secretion or nutrition, there taking up products destined either for excretion or for further elaboration. In order that these constant cell changes, this production of secretion and excretion, these processes of elaboration and assimilation, which constitute the actual art and method of life, should go on, the presence of nitrogen is necessary. Hence one of the great uses of albuminates in the food is to provide the nitrogen necessary to promote the changes of nutrition in the body. This process is called metabolism. Thus we see that albumen is a necessary food, not only in that it repairs tissue waste, but also because it plays a large part in the production of functional activity and energy. Without albumen, the rapid tissue changes necessitated by great activity of body could not take place; hence races and persons who live on a non-albuminous diet are inert, wanting in vigour and initiative. Change their diet and you are often able to change their character. Thus the potato-fed Irishman, on his damp soil, is said by those who employ him in manual labour to have " no heart in him "; but transport him to a stimulating climate, and make of him a beef-fed American, and his energy becomes sustained and even sometimes excessive. Albumen is, moreover, capable, it seems, of being split up by the agency of the cells in the body into nitrogenous and non-nitrogenous principles; for we find that when an animal has been fed exclusively on albumen, both fat and sugar have been produced from this food within the body, and hence it is possible that albumen may under certain conditions also play the part of a force-producer, force being produced, as I will show later, by the combustion of fat and sugar in the body.

To sum up: The uses of albuminates in the body are threefold, viz.: (1) To repair the waste of those tissues which contain nitrogen, viz., the muscles, nerves, brain, etc., and to reconstitute the secretions and fluids of the body, and the digestive juices; (2) to control, stimulate and support the vital processes of functional activity and nutrition, and to promote oxidation in the body; (3) to contribute to the development of muscular and nervous energy, by splitting up into nitrogenous and non-nitrogenous elements, by the production of heat, and under certain conditions by the formation of fat.