Whenever an individual is overnourished - immaterial whether the caloric surplus is furnished by proteids, fats or carbohydrates - it will be found upon investigation of the nitrogen balance that a certain amount of nitrogen is retained in the body. Many hundreds of exact studies of this kind that, of course, cannot be carried out in general practice, but that offer no difficulties in a clinic or a laboratory, have been made. Whereas the fact is established that under the influence of overfeeding nitrogen retention occurs, the significance of this factor has not yet been cleared up and there is still much discussion on this subject. When the science of metabolism was still in its infancy an explanation was promptly forthcoming, for the investigators of that time simply calculated the retained nitrogen as albumen and later as muscle tissue according to the following figures:

1 g of retained N = 6.25 g of albumen = 29.4 g of muscle tissue

Doubts in regard to the validity of this explanation were expressed early by the father of the science of metabolism, C. von Voit, for he recognized the uncertainty of the explanation that the nitrogen retention could be interpreted directly as a gain in muscular tissue. The same investigator also noticed how easily later on, when the ingestion of food was reduced, this retained nitrogen was again eliminated. This phenomenon was in marked opposition to the ordinary observation in cases of normally fed or undernourished individuals in whom upon the reduction of the proteid ration the organism very obstinately retained its nitrogen (compare first lecture). Voit constructed the conception of labile so-called "circulating albumen" in contradistinction to a more stable "organ albumen." Before this time proof had been furnished that any albumen acquired by overfeeding was not found present in the circulating fluids of the body. Later (in 1893) I formulated the hypothesis that the retention of nitrogen actually represented a building up of albumen, but that this albumen was stored in the cells themselves as "so-called reserve albumen" similarly to glycogen and fat that can also be deposited in the cells as reserve material. I expressed the opinion at the time that the albuminous reserve material contained in the cells could impossibly possess the viability and the value of protoplasm proper and could not participate like the latter in the transformation of energy. For this reason I coined the word "dead cell inclosures"; this expression has been thoroughly misinterpreted by other writers. I confess that it was not very happily chosen, because one can hardly designate any constituent of the living body as "dead." The sense, however, in which the word was employed should have been altogether clear, and later investigations, as I will have occasions to show, endorsed the views expressed by me at the time. Now-a-days there is no doubt whatsoever that the nitrogen retention seen in overfeeding really indicates a true addition to the albumen stores of the body and that the cells are the depot in which this excess albumen is stored. A small portion of this retained nitrogen is possibly built up no further than to the stage of certain precursors of the albumen molecules that, like the first disintegration products of the albumen molecule, may be designated as peptids and polypeptids.

The amount of nitrogen that can be retained in the body by overfeeding varies. The quantity of retained nitrogen is dependent - leaving aside certain important factors that are to be discussed later - chiefly upon the amount of albumen introduced, the kind of albuminous food offered and the degree of the caloric surplus. If the diet contains much albumen, and especially if the albumen it incorporates consists chiefly of casein (or nutrose, plasmon or nucleo proteids) then the increase of body albumen becomes particularly great. If there is a preponderance of meat, and especially of eggs and vegetable albumens among the albumens of the diet, then the building up of body albumen is smaller. When all the contributing factors are favorable one may count upon a daily retention of from 5 to 6 gn (albumen 31 to 38 g). In ordinary fattening cures with a moderate albumen ration (about 100 to 120 g daily) and a moderate caloric surplus (of 30 to 40% above the calculated amount of the maintenance diet) one may expect to find a daily retention of nitrogen of from 1 to 3 g; if the caloric surplus is from 40 to 60% above the maintenance diet, one may expect a retention of from 2 to 6 g of nitrogen per diem. Calculated for each day this appears a very small sum; if this factor is repeated for long periods of time, however, very considerable additions result.

In an experiment carried out with painful accuracy by my former assistant, L. Mayer, 383 g. of nitrogen were retained during a period of 62 days. Using the ordinary method of calculation, one finds that from this amount of nitrogen can be calculated the retention of 2394 g of dry albumen or of 11.26 kg of meat (cellular substance). The individual upon whom this test was made was, prior to the beginning of the experiment, in a fairly good state of nutrition and the attempt to fatten him was made only for the sake of the experiment and with his full consent. The body weight increased during the experiment from 56.0 kg to 69.5 kg.

Two important observations have been made in regard to nitrogen that has accumulated in the body in this way by overfeeding. The first of these observations is of constant occurrence; the second one, requiring for its verification an enormous amount of tedious work, has been verified only once (namely, in the above quoted experiment of L. Mayer).

1. The nitrogen bodies (or as we may say with equal safety), the albumen that has been accumulated in this way, does not show a great tendency to remain in the body; in other words, it does not "stick" very hard. As soon as the albumen ration or the amount of nitrogen-free food is reduced a large proportion of the previously accumulated nitrogen reappears in the urine as urea. The individual for instance upon whom Mayer experimented eliminated 24 g of nitrogen in the urine during the 21 days following the experiment, although the diet still contained the considerable sum of from 100 to 118 g of albumen and although pabulum representing in its totality an average value of 43 calories pro kilo was being introduced; in other words, really more than would correspond to the calculated caloric requirement of an individual remaining in one room and performing a very small amount of physical labor. Newer experiments therefore completely corroborate the find ings of C von Voit's animal experiments (see above). It would be important to determine by a prolongation of these experiments (for instance by prolonging the so-called after-period that sets in as soon as the fattening period is terminated) how long the accumulated albumen really remains in the body. So far no investigation has been continued for a sufficiently long time to enable us to arrive at definite conclusions in regard to this point. This much remains established, however, that a large portion, possibly all of the albumen that is accumulated in the organism of an individual who was previously well nourished, does not possess the same stability as the albumen that was originally present in the body. It is probable that the physiologic dignity of the latter albumen is not as great as that of the former.