676 NUTRITIVE INGREDIENTS AND VALUES OF THE FOOD WE EAT. 



nearly accurate determination. Indeed, the per- 

 centage of the more important constituents 

 of various foods actually digested by domestic 

 animals of different species, breeds, sexes, and 

 ages, and under varying circumstances, has 

 been a matter of active experimental investiga- 

 tion in the German agricultural-experiment sta- 

 tions during the past twenty years. Briefly ex- 

 pressed, the method consists in weighing and 

 analyzing both the food consumed and the solid 

 excrement, which latter represents the amount 

 of food undigested, the difference being the 

 amount digested. Between one and two thou- 

 sand such series of experiments have already 

 been reported. The data thus accumulated 

 enable us to construct tabular statements of the 

 digestibility of a great variety of feeding-stuffs 

 by ordinary animals, as horses, oxen, cows, 

 sheep, and swine. 



Such experiments upon human subjects, 

 however, are rendered much more difficult by 

 the necessity of avoiding complex mixtures of 

 foods, in order that the digestibility of each 

 particular food or food ingredient may be de- 

 termined with certainty, and the fact that it 

 is not easy to continue to eat the same kind of 

 food long enough for a satisfactory experiment. 

 No matter how palatable a simple food may be 

 to a man at first, it has been found that it will 

 almost certainly become repugnant to him 

 after four or five days. In consequence, the 

 digestive functions are disturbed, and the ac- 

 curacy of the trial is impaired. In the experi- 

 ments now in question, it was quite exceptional 

 to find persons, in any walk of life, who could 

 continue to eat large quantities of simple, plain 

 food for tolerably long periods a fact, by-the- 

 way, which strikingly illustrates and empha- 

 sizes the importance of a varied diet in ordi- 

 nary life. 



* Protein. 



A considerable number of experiments have, 

 however, been carried out, notwithstanding 

 these difficulties, and have given us definite 

 results of no little interest. In an article in the 

 "American Agriculturist," on the "Amounts 

 lost from Various Foods through Non-Assimila- 

 tion," Professor Storer, of the School of Agri- 

 culture of Harvard University, has given the 

 preceding table, based principally upon results 

 of a very elaborate research by Rubner, of 

 Munich. 



This subject is so important, and withal so 

 new to those who do not follow closely the 

 results of the latest foreign research, that we 

 quote further from the article referred to : 



It is to be observed that the figures of the second 

 column of the table give no more than an approximate 

 idea of the value of each of the foods enumerated. A 

 more precise conception of these values may be had 

 by comparing the figures of column two with those in 

 the third and fourth columns, which give the percent- 

 age amounts of nitrogen and of carbohydrates that 

 have escaped assimilation. It is noteworthy that the 

 chemical composition of dung is often very unlike 

 that of the food from which it has been derived. It 

 does,not at all follow, for example, that the dung will 

 be highly nitrogenized when food has been eaten 

 which is particularly rich in nitrogenous constituents, 

 for it may happen in this case that a large portion of 

 the nitrogen is voided in the urine. Rubner found, 

 for instance, 6* per cent of nitrogen in dry excrement 

 from a meat diet, though the flesh had contained 14 per 

 cent of nitrogen ; in dry excrement from milk he 

 found but little more than 4 per cent of nitrogen ; 

 while he found as much as 8 per cent of nitrogen in 

 the excrement from white bread, which, as compared 

 with meat and milk, is a substance to be regarded as 

 poor in nitrogen. On referring to column four of the 

 table, it will be seen that much larger amounts of 

 nitrogen went to waste in the case of vegetables which 

 were themselves poor in nitrogen than in that of the 

 so-called animal foods, such as flesh, eggs, and milk, 

 which contain a large proportion of this element. In- 

 deed, it is probable that the nitrogen in the animal 

 foods is really assimilated well-nigh completely, and 

 that the larger part of what little nitrogen is actually 

 found in the dung from such foods is actually part 

 and parcel of certain biliary products, secreted from 

 the body, which have done duty in the process of di- 

 gestion. In this view of the matter, sucn excremental 

 nitrogen can not properly be classed with that wasted 

 from the food through non-assimilation. Some of this 

 biliary nitrogen occurs, of course, in all excrement, 

 about as much, in one kind as in another, and a mental 

 reservation must always be made on account of it. 



Several curious points of detail have been noticed in 

 these researches. It appears, for example, that hard- 

 boiled eggs are assimilated by healthy men just as 

 completely as roast beef is ; though it may none the 

 less be true that the flesh is digested and assimilated 

 in less time than the egg, and that the organs of di- 

 gestion are put to less trouble in dealing with it. It 

 has been shown also, by several different observers, 

 that bread alone is an insufficient food. On a bread- 

 diet the body gives out each day more nitrogen than 

 is assimilated from the food, and the coarser tine bread 

 so much the worse for the consumer. It appears from 

 the table that milk is not so completely assimilated by 

 adults as would have been supposed at first sight. 

 Milk is distinctly inferior to beef and eggs in this 

 respect, and is even worse than some of the foods of 

 vegetable origin. The reason of this peculiarity ap- 

 pears to depend in good part upon the large_ amount 

 of ash-ingredients that are contained in milk, and 

 which are not assimilated by the body. This remark 

 applies particularly to lime, which is abundant in 

 milk, and which passes out from the body in the solid 



