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the carbonaceous compounds in fatty constituents is about two and a half times as great as that of the saccharine constituents, it is evident that, in framing a table of alimentary equivalents, the amount of carbon must be stated as having the same nutritive value throughout. In the following table, therefore, which is given by Dr. Letheby in his valuable work on Food, the amount of carbonaceous matters in the different articles of diet is estimated as starch
As this table contains almost all the articles which are likely to be met with in a common dietary, it becomes no difficult matter to calculate the total amount of carbon and nitrogen which any such dietary yields, and to compare the results with other dietaries that have been calculated in the same way. It is neces
sary to add that the nutritive equivalents apply to articles in their uncooked state, and that the meat is boned.
SECTION III.-FOOD AND WORK.
It has already been stated that, in addition to maintaining the body in a healthy state, the potential energy of food is the sole source of the active energy displayed in mechanical motion or work. It therefore follows that the diet must be increased as the work increases; and the question arises at the outset,—What is the minimum amount of food on which a man of average size and weight can subsist without detriment to health? From a large number of observations made by Dr. Lyon Playfair and others on the dietaries of prisons and workhouses, and by Dr. Edward Smith on the amounts of food consumed by the Lancashire operatives during the cotton-famine, it would appear, according to Dr. Letheby, that a barely sustaining diet should contain about 3888 grains of carbon, and 181 grains of nitrogen. In round numbers, and taking a somewhat liberal view of the question, Dr. Edward Smith has proposed the following averages, as representing the daily diet of an adult man and woman during periods of idleness:
Taking the mean of all the researches which have been made by eminent physiologists, Dr. Letheby gives the following as the amounts required daily by an
adult man for idleness, for ordinary labour, and for
And here it may be observed that the general correctness of these averages is fully borne out by the results of the numerous experiments which have been made to ascertain the amount of carbon and nitrogen actually excreted by adult men under different conditions of diet and exercise. These results have also been summarised by Dr. Letheby, and the averages are found to correspond very closely with those just given, thus:
The actual amounts of carbonaceous and nitrogenous matters which are consumed by low-fed and well-fed operatives are given in the following tables :
Weekly Dietaries of Low-fed Operatives, calculated as Adults (Dr. E. SMITH).
Potatoes. Sugars. Fats. Meat. Milk. Cheese. Tea.
Daily Dietaries of Well-fed Operatives (PLAYFAIR).
As an addendum to these data, and by way of contrast, I may here give some particulars with reference to the dietaries of the convicts confined in English prisons. In the hard-labour prisons, where the great majority of the prisoners are employed at active outdoor work, there are two scales of diet-viz., the lightlabour diet and the full-labour diet. I have carefully calculated the nutritive values of the various articles of food contained in these diets, according to the equivalents given in a preceding table, and the results are as follows: