CHEMISTRY OF DIGESTION AND NUTRITION. 367 



In Voit's diet, which is the one usually taken to represent the daily Deeds 

 of the body, it will be noticed that the ratio of the nitrogenous to the non- 

 nitrogenous food-stuffs is about as 1 : 5, and basing the estimate upon a man 

 weighing 70-75 kilos., 118 grams of proteid per day would represent a 

 consumption of proteid equal to 1.3 to 1.7 grams per kilo, of weight. 

 Siven 1 has recently attempted to show that this proportion of proteid in food 

 is unnecessarily high. In some experiments upon himself he was able to 

 reduce his daily proteid food to about 0.2 gram per kilo, of body weight 

 and still maintain his body in N-equilibrium, provided the non-proteid por- 

 tions of his diet were so increased that the total energy of his daily diet 

 remained unchanged. Whether or not so high an amount of proteid per day 

 as 118 grams is most beneficial to the body, under normal conditions of mod- 

 erate labor, is perhaps an open question. It seems certain that for short 

 periods at least the average individual can keep his body in equilibrium on 

 much smaller amounts. It must be remembered, in regard to these diets, 

 that the amounts of food-stuffs given refer to the dry material: 118 

 grams of proteid do not mean 118 grams of lean meat, for example, since 

 lean meat (flesh) contains a large proportion of water. Tables of analyses of 

 food (one of which is given on page 278) enable us to determine for each par- 

 ticular article of food the proportion of dry food-stuffs contained in it, and in how 

 great quantities it must be taken to furnish the requisite amount of proteid, 

 fats, or carbohydrates. There is, however, still another practical consideration 

 that must be taken into account in estimating the nutritive value of articles 

 of food from the analyses of their composition, and that is the extent to which 

 each food-stuff in each article of food is capable of being digested and absorbed. 

 Practical experience has shown that proteids in certain articles of food can be 

 digested and absorbed nearly completely when not fed in excess, while in other 

 foods only a certain percentage of the proteid is absorbed under the most favor- 

 able conditions. This difference in usableness of the food-stuffs in various 

 foods is most marked in the case of proteids, but it occurs also with the fats 

 and the carbohydrates. Facts of this kind cannot be determined by mere 

 analysis of the foods; they must be obtained from actual feeding experiments 

 upon man or the lower animals. ft has usually been stated by those who 

 have worked in this field that the proteids of meats are more completely util- 

 ized than those of vegetables. Hut it is possible that as a generalization this 

 statement is too sweeping, and rests upon the erroneous assumption that the 

 nitrogen in \\'c<^ represents chiefly undigested proteid. Prausnitz 2 and 

 others have given reasons for believing that the nitrogen inthefeces is derived 

 mainly from the intestinal secretions, and that vegetable foods that do not 

 contain much indigestible material, such as rice and bread, are practically 

 completely digested and absorbed in the intestines, their proteids, therefore, 

 being utilized as completely as in the case of meats. Munk' 1 gives an inter 



1 Skandinavisehes Archivfiir Physiologic, 1899, Bd. 10, S. 91. 



1 Zeitsehrifi fur Biologie, L897, Bd. 35, S. 835. 



3 Wevl's Handbuch der Hygiene, L893, Bd. iii. Theil i. S. 69. 



