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 :

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:

Light-labour diet
Full-labour diet

DAILY AVERAGE.

What is called light labour applies to manual work requiring very little muscular exertion, while full labour embraces a variety of occupations, such as tailoring, shoemaking, artisan work, and navvy work. From the averages already given, it will be inferred that the light-labour diet is quite sufficient for the easy nature of the work, and, practically, with few exceptions, this is found to be the case. The prisoners employed at light labour are all more or less invalid or crippled, and although almost all of them could take more food, they are not found to lose weight, except in isolated cases. With regard to the practical working of the full-labour diet, however, this much cannot be said; for while prisoners employed at comparatively easy labour, such as artisan work, do not lose weight to any extent, those employed at the more arduous kinds of labour, such as navvy work, almost invariably lose a great deal, and after a time must be removed to lighter work to recruit. In whole gangs of prisoners employed at filling and wheeling barrows of clay, for example, I have found an average loss of weight of over 13 lbs. per prisoner, the loss accruing within a period of about two months after they had been put to such work. The consequence is, that in a hard-labour prison the convicts must be continuously shifted from hard to lighter work, and, after recruiting, from lighter to hard, otherwise they would completely break down, on account of the insufficiency of the full-labour diet for the severer kinds of prison labour. In military prisons, according to Dr. Letheby, where the dietary contains as much as 5090 grains of carbon and 256 grains of nitrogen daily, even for short periods of confinement, many of the prisoners lose weight, and give evidence of other signs of decay, so

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