COMPOSITION OF FOODSTUFFS. 873 



On the whole, however, the above proportions are found to be fairly well 

 maintained, the ratio of carbohydrates to fats in the diet varying more 

 than the proportion of proteid to non-proteid material. As a general 

 rule, it will be found that with the more wealthy classes there is a 

 relatively greater amount of proteid and fat as compared with carbo- 

 hydrates ; whereas with the poorer classes the carbohydrates increase in 

 proportion, and the proteids and fats diminish. With a diet composed 

 of vegetable matter alone, the proportions are liable to be considerably 

 modified, since, in order to obtain a sufficient amount of proteid from 

 most vegetables, a much larger proportionate amount of carbohydrate 

 food is inevitably consumed. On the other hand, since with flesh food 

 the amount of proteid necessary for carrying on the metabolic processes 

 of the body is much more easily obtained than from vegetable food, 

 and since flesh food invariably contains a considerable amount of fat, 

 the proportion of proteid and fat to carbohydrate is apt to be much 

 greater than the normal when the diet is mainly composed of animal 

 matter. 



For the determination of the value of the chief organic materials of the 

 foodstuffs in nutrition, the most important point to be ascertained regarding 

 their composition is the amount of nitrogen and carbon in each. In round 

 numbers, this may be stated as follows : Proteids contain 15 to 17 per cent. 

 N, and 50 to 55 per cent. C l ; animal fats, on an average, 76 '5 per cent. C ; and 

 carbohydrates, such as starch and sugar, 40 to 45 per cent. C. Since the amounts 

 of proteid fat, and carbohydrates in all the ordinary foodstuffs has been accur- 

 ately determined, 2 and is given in the form of tables, it is not difficult, if the 

 amounts of each which are ingested are carefully weighed, to determine by 

 calculation the total K" and C of the ingesta. For very accurate work, 

 however, it is necessary to make direct determinations of the N and C in 

 the food taken; this is effected by ordinary chemical methods (that of the 

 nitrogen usually by Kjeldahl's method). 



The amount of flesh or fat which is at any time becoming lost or laid on 

 can be easily approximately determined by an examination of a balance table, 

 for the nitrogen in the urine represents metabolised proteid, the amount 

 of which is arrived at by multiplying the numbers of grms. of nitrogen found 

 by 6'25 (since proteids contain 16 per cent. N). Since any excess or deficit 

 of proteids represents flesh lost or laid on, the amount of such loss or addition 

 can be directly obtained by taking each gramme N in excess or deficit to 

 represent 30 grms. flesh (since flesh contains about 3 '4 per cent. H") (Voit). 

 And, after reckoning off the carbon which the proteid metabolised would contain 

 (53 per cent.), any further excess or deficit of carbon in the ingesta would 

 represent the carbon of fat lost or laid on, and the amount of this may be 

 approximately obtained by multiplying the number of grms. of carbon in the 

 excess or deficit by 1'3 (since fat contains about 7 6 '5 per cent, carbon). Thus, 

 in the balance table on p. 872, the man under observation retained 39*8 grms. 

 C, representing 52 grms. fat laid on. 



The following table (from Bunge) gives the percentage composition of 

 some of the chief foodstuffs ; the remainder in each case is mainly water with 

 a variable amount of salts the numbers are taken from Kb'nig. They are 

 given in inverse order to the proportion of proteid they contain : 



1 Argutinsky determined the percentage composition of beef, completely divested of fat 

 and dried, to be as follows : C 49'6, N 15'3, H 6'9, + S 23 '0, ash 5'2 (Arch. f. d. ges. 

 Physiol, Bonn, 1893, Bd. Iv. S. 345). 



2 Konig, "Chemie der menschl. Nahmngs-u. Genussmittel," Berlin, 1882, Aufl. 2. 



