So long as the food is suited to the individual capacity and idiosyncrasy it is really immaterial for fattening purposes whether we depend upon protein, carbohydrates, or fats. Proteins are certainly the least useful, for besides 12-15 per cent. - much beyond the average - which is lost in their digestion and absorption, some of their energy is dissipated in increasing the oxidation processes, an operation designated by Rubner as their dynamic action. The amount capable of being added to the diet is also limited because of their tendency to diminish the appetite, and no advantage is obtained by employing the various concentrated proteins, although the soluble varieties are more helpful than the insoluble.

Carbohydrates are more useful, but on account of difficulty in their assimilation they cannot be increased indefinitely. Altogether 25 per cent. of their value is lost, including 10 per cent. in their digestion and absorption, and a considerable percentage of heat which is wasted during their transformation into fat. When combined in an agreeable manner with fats, e.g., porridge, or a breakfast cereal and cream, or in the form of extract of malt, they are much more easily utilised. In any case it must always be remembered that carbohydrates are protein - and therefore tissue - saving. Employed as fattening agents in animals, they frequently produce fatty degeneration of the heart, and this is an additional reason for not placing too much reliance upon them for augmenting the deposit of fat.

Of all food-stuffs, however, fat is the one best fitted for increasing the store of adipose tissue, not only on account of its high calorific value, but because it sustains practically no loss of energy in its passage through the alimentary canal, not more than 2 1/2 per cent. being dissipated in the process of digestion and absorption. It is a truism that people who are fond of fat never require a rest cure, and in this connection it is worth while pointing out that Voit's standard of 56 grams is decidedly too low, and that 100 grams should be the minimum daily allowance of fat in any dietary. This quantity may easily be trebled during forced feeding if personal idiosyncrasy be taken into consideration, but in any case at least 200 grams should be insisted upon. It is wise not to give it in an unusual form, but to adhere to the kind commonly included in the diet list, such as butter, milk, and cream, because these may be continued as an increased ration long after the formal cure has ceased.

The fattening properties of alcohol being indirect, and in the nature of a diminution of the metabolic powers, and the general effect being toxic, it is injurious to rely upon this agent in ordinary circumstances.

Recognising these facts, it is usually a very simple procedure to enable a patient suffering from any form of chronic under-nutrition to increase his weight and strength, and although in severe cases of nervous exhaustion it is, perhaps, essential still to prescribe a complete rest-cure of the Weir Mitchell type, with isolation, perfect rest in bed, and passive exercise in some form, it is rarely necessary to recommend such an expensive form of treatment, excellent results being obtained by a modification of the process. This is specially the case in those who have lost weight, and become anaemic from constant dyspepsia, due in a great measure to a certain degree of gastroptosis, and whose digestion is effective or otherwise according to the efficiency of the motor power of their stomach. This, again, is a fluctuating quantity, dependent on the amount of nervous energy dissipated in the day's work. In such patients a considerable proportion of the food undergoes a process of degradation from its long retention in the stomach, and is quite incapable of advantageously nourishing the tissues. Hence when they can take a sufficiency of nutriment they are unable to obtain its full caloric value, although very little research has been made into the nature of the end-products of the food-stuffs in such cases. It is known, however, that in addition to the damage to the tissues by the nutritive loss, there is formation of toxins, the absorption of which is productive of the profound depression so constantly observed in dyspeptics.