On the other hand, however, the question was raised whether the excess of the fat in the food is really deposited as body fat in the or ganism, and whether it is not rather the fat in the food which is de composed and only that fat is stored up which is formed from the decomposed albumin. It was necessary, therefore, to furnish the proof that fat likewise, if fed in excess, may be directly deposited in the animal body, and this proof could be supplied only by feeding with a fat which does not occur in the animal body and whose sub sequent accumulation alongside of the animal fat was to be dem onstrated. Experiments in this direction were first undertaken at Kiihne's instigation by Radziejewski, who fed with rape oil, but with out obtaining decisive results. Later on Lebedeff succeeded in caus ing the deposition in the dog both of the tallowy hard sheep's fat and of the liquid linseed oil supplied in the food. The question was finally decided only by J. Munk, who showed that after feeding for two weeks with rape oil along with a little albumin there was depos ited in the body of a dog nearly 1.5 kgm. of an oily fat in which also the characteristic constituent of rape oil, erucic acid, could be recog nized. Thereby the transition of the food fat into body fat was set tled beyond a doubt. Ebstein's view, that fat in the food does not give rise to fat-formation, is one directly opposed to all physiological investigations, and, as Zuntz has arisen only from a mis understanding of one of Voit's statements, whose interpretation in Ebstein's sense has been particularly cautioned against by Voit him self, for which reason it may be passed over as unscientific.
According to Pettenkofer and Voit, the carbohydrates contribute in the main indirectly to the formation of fat. Being easily decom posed, they may even in the largest quantities be completely oxidized into carbonic acid and water, and thereby save both the fat of the food and that formed from the altered albumin from decomposition. Further experimental investigations, however, by Weiske and Wild, Soxhlet, Meissl and Strohmer, J. Munk, M. Rubner, and others have definitely proved also that fat is formed in the animal body directly from carbohydrates.
The fat-formation in the human body is therefore amply provided for by the food in its varied composition. Body fat may be devel oped from the fat ingested in the food, even from the preformed fatty acids or those derived from the fats and soaps, as well as from the carbohydrates and the albumin. Voit has calculated that a forma tion of fat occurs in a man at rest or doing little work whenever he ingests along with a sufficient quantity of albumin (118 gm. daily) more than 259 gm. of fat, equivalent to 024 gin. carbohydrates, or more than 100 gm. fat and 385 gm. carbohydrates. When this quantity is permanently exceeded, some fat is daily deposited so that in the course of time the accumulation of fat may become quite large.
b. Insufficient Utilization. of .3faterial.—The body fat and the fat
forming substances ingested in the food, together with the carbona ceous decomposition products of albumin, are more or less completely consumed in the animal economy for the production of force and heat, in which case they are split up into carbonic acid and water. The amount of the fat combustion is nearly proportionate to the labor performed. All the physiological functions, too, are effected with a decomposition of fat, and the production of heat is directly dependent upon it. The greatest combustion of fat and fat-forming substances is required for muscular labor and may rise, according to the extent of the work, to more than double the normal fat trans formation occurring at rest. It is true, Pfliiger and his pupils, Krummacher and Argutinsky, have recently felt compelled, on the strength of their experiments, to assert that the muscle works with albumin; but von Noorden and Munk have pointed out the errors in their observations, since the increase of albuminous transformation in Pfhiger's experiments was dependent upon the deficit in calories and thus was only loosely connected with the muscular labor as such (Munk). Pflfiger's view, that the albumin is -the source of the force, is vitiated, according to von Noorden, even by the calculation which shows that men utilizing day by day more than half of the entire calorie transformation in muscular labor, ingest year after year at most 14 to 18 per cent. of the entire calorie value as albumin in the food. In view of this fact, the assertion that albumin is the source of muscular force. would contravene the law of the conservation of energy.
As in the requirements of active labor, so where greater heat for mation is called for, more fat must be used up. This is in harmony with the experiments which show that a low temperature of the sur rounding air raises the combustion of fat, while it has no influence upon the of albumin. For this reason a diet suitable for the requirements of winter will lead to the deposition of fat in the summer.
We know from the experiments by Bedard, Moleschott, Pfliiger, Voit, and others that the most variable stimuli acting upon the sen sort' nerves are followed by an increased metabolism which is associ ated with augmented decomposition of fat, while the intensity of the metabolism is materially lessened when such influences are absent. The cessation of sexual activity in animals after castration hastens their fattening, according to the experience of cattle breeders (see above). In accordance with these facts, too, the decomposition of fat is at the minimum during sleep. In Liebermeister's experiments the excretion of carbonic acid per hour sank during sleep from 32.8-33.4 gin. to 24.6 gm. From this fact Lobisch calculates that a person who changes his mode of life, the supply of food remaining the same, by sleeping eight hours instead of seven, accumulates in the course of a year 1 kgm. 43.9 gm. (about 24- pounds) more fat in the body.