136 



KNOWLEDGE 



[July 1, 181)8. 



or at least for practical purposes may be reckoned under a 

 few heads. Thus — 



Foodstuffs are — 



1. Albuminoids and other substances containing 



nitrogen. 



2. Fat, starch, and sugar. 



3. Mineral substances, chiefly common salt and phos- 



phates. 



4. Water. 



5. Food adjuncts. 



The principal functions of the above classes of food- 

 stuffs are as follows : — 



1. Albuminoids, &c., are oxidized by the air which is 

 inhaled into the body, and go to form the muscle and 

 flesh. The process of oxidation gives out heat, and hence 

 these rlesh-forminfi foods assist also to keep up the heat of 

 the body. 



2. Fat, starch, and sugar are oxidized in the body, 

 thereby acting as lient (/iirrs, but they do not form muscle 

 and flesh. In hard bodily work it is necessary to increase 

 the supply of heat-giving food. The waste of muscle and 

 flesh does not increase with increased bodily labour in 

 nearly the same proportion as does the demand upon the 

 heat of the body. Fat has about 2i times the warming 

 power of starch and sugar, there being a larger proportion 

 of carbon and hydrogen to be oxidized. Hence fat is the 

 principal food-stufi' to be added to the diet to meet the 

 demand of extra bodily work or the corresponding tax of a 

 colder climate. Fat can be stored up in the body (as a 

 layer under the skin), where it acts as a store of heat- 

 giving material which can be drawn upon as required by 

 the system. 



3. Of the mineral substances taken into the body the 

 lime salts and phosphates form the solid fabric of the 

 bones. 



4. Water constitutes about two-thirds by weight of the 

 substances of the body. The water taken in as food is 

 required both as a constituent of the body and also as a 

 carrier of food in and through the system. 



5. Food adjuncts are of importance more on account of 

 their efi'ects (whether stimulating or sedative) upon the 

 nervous system and on account of their effect on the palate 

 than for any actual power of nourishing or sustaining the 

 fabric of the body. The most important are alcohol, and 

 the alkaloids contained in tea, coffee, and cacao. 



The daily ration of an adult under ordinary conditions, 

 according to Prof. Church, should contain the dift'erent 

 food-stufts in about the following quantities : — 

 Daily Ration. 



1. Water . . . 88-66 oz. avoirdupois 



2. Albuminoids . . 4-25 ,, 



3. Starch and sugar . 11-40 ,, 



4. Fat . . . 3-77 



o. Mineral food . . 1-03 ,, 



10911 

 The small quantity of food adjuncts is not included in 

 the above table. The actual weight of food eaten will 

 exceed the above total by about one ounce on account of 

 ttbrous material, either vegetable or animal, which is taken 

 with the food, but which is not assimilated by the body. 

 The food-stufi's 3 and 4 have the same function, viz., 

 that of keeping up the heat of the body. Weight for 

 weight, fat has about '2} times the heating power of starch. 

 As starchy and fatty foods are to some extent inter- 

 changeable in diet, a convenient way of expressing the 

 daily ration is to multiply the amount of fat by 2-!,, which 

 gives the quantity of starch equal to the fat in heat-giving 

 value. In the above case the amount of fat is 3-77, which. 



multiplied by 2j, gives 8-8, which, added to 11-40, the 

 amount of starch and sugar, gives a total of 20-2 ounces 

 of heat-giving food reckomil as sUiirh. We may, therefore, 

 write the daily ration thus — 



Water. ricsli-fonuers. / , ,"" ,' , ■, Minerals. 

 ( reckoned as starcU). 



88-66 4-25 20-2 1-03 



Let us now return to the practical calculation of the 

 quantities of the food-stuft's contained in a day's diet, the 

 weight of which we have supposed to be taken during 

 meals by aid of the spring letter-balance. This may be 

 done by setting out the results of the weighings in a 

 tabular form as follows : — On the left, in the first vertical 

 column, set down the names of the various foods eaten ; 

 bread, butter, milk, &o. In column 2 set down opposite 

 the names of the foods the weight of each which has been 

 eaten during the day. In some work on the chemistry 

 or the composition of foods find the percentage com- 

 position of the food eaten, and hence calculate the weight 

 of each food-stufl' in the several articles of food taken. 

 Enter the water in vertical column number 3, the flesh- 

 formers in column 4, the heat-formers in column 5, 

 and the minerals in column 6. The vertical columns 

 are then added up and we obtain at the foot of 

 column 2 the total weight of food taken, and at the 

 foot of the other columns the total weight of each food 

 stufl". It then remains to compare the results obtained 

 with the standard ration given above, or with some otlier 

 ration suited to the particular nature of the daily employ- 

 ment of the person. Of course it is not only the quantity 

 of the food-stuft's which has to be taken into account in 

 judging whether the diet is a suitable one or not: we must 

 also take account of the proportion between the amounts of 

 the dift'erent f'ood-stufl's. The most important ratio, the 

 actual value of which should, however, depend upon the 

 amount of bodily work done, is the ratio of flesh-formers 

 to heat-givers. If the fat be calculated according to its 

 " starch equivalent," the ratio should be about l:4f. The 

 ratio of flesh-formers to heat givers is termed the nutrient 

 ratio, and a table of the nutrient ratio of dift'erent classes 

 of food IS a valuable guide in the determination of a diet. 

 Such knowledge is absolutely necessary where a uniform 

 diet has to be prescribed for persons who are not at liberty 

 to select and vary their food according to their inclination, 

 as, for instance, prisoners. Generally speaking, the flesh- 

 forming foods containing nitrogen are the most expensive. 

 Nitrogen, though so abundant in its uucombiued and inert 

 form in the air, generally becomes expensive when wanted 

 for any useful purpose, whether as manure for the land or 

 as food for man. How this curious fact comes about we 

 hope to have another opportunity of explaining. The most 

 important flesh-formers are the lean of meat and green 

 vegetables. The starchy foods, as rice and potatoes, are 

 generally speaking cheap and easily obtained. The fat of 

 meat supplies the heat-givers in a more concentrated form, 

 though not so cheaply. The form in which the various 

 food-stuft's may be taken must depend largely upon the 

 mode of life. Thus, a labouring man who works in the 

 fields may make his dinner off a dish of cabbage and fat 

 bacon, deriving the flesh-formers from the vegetable and 

 the heat-givers from the animal food. For men of seden- 

 tary habits such a combination would be scarcely suitable. 

 A lean chop with potatoes^ — a very usual luncheon for a 

 business man — supplies the same food-stuft's in a lighter 

 form. In this case the flesh-formers are derived from the 

 animal food and the heat-givers from the vegetable. 

 Needless to say, this is a more expensive meal than the 

 first. Cheese is one of the cheapest forms of nitrogenous 

 food, and may be taken as a substitute for lean meat. 



