Chap, v.] NUTfilTIOK 667 



to the dominion of foreign organisms than even to that of the 

 body itself, though these opportunities are less than with a cor- 

 responding mass of animal origin. With respect to these three 

 features then, the strictly vegetarian diet seems, on physiologi- 

 cal grounds, inferior to one of a mixed nature. There are as we 

 said other aspects, still of a strictly physiological kind, to be 

 considered, such as the relative digestibility of vegetable articles 

 of food, the relative metabolic value of the food-stuffs of vege- 

 table origin, and the influence of animal extractives; but any 

 fuller discussion of these points would be out of place here. 



§ 444. We have treated the diet discussed above as a normal 

 diet, suitable for man under ordinary or general circumstances. 

 Ought such a diet to be modified for the various exigences of 

 life such as labour, age, climate, and the like? 



We shall discuss the influence of age in the concluding por- 

 tions of this work. 



We may be inclined at first sight to assume that the total 

 amount of the diet should vary with the weight, that is the size 

 of the individual; and indeed in discussions on nutrition, state- 

 ments concerning metabolism and amount of food are often 

 given in terms of per kilo of body weight. In a broad sense it 

 may be true that a small man needs less food than a large one; 

 but it must be remembered that, as we saw in speaking of animal 

 heat, the smaller organism, having the relatively larger surface, 

 carries on a more rapid metabolism per unit of body weight, 

 and so needs relatively more food. And moreover the influence 

 of size is probably far less than the influence exerted by the 

 inborn individual characters of the organism, giving rise to 

 what we may call the personal equation of metabolism. The 

 smaller metabolism of woman, leading to the use of a scantier 

 diet, as compared with that of man, is to be regarded in this 

 light rather than with reference to the average lesser weight of 

 woman. The relative metabolism of the two sexes may be illus- 

 trated by the case of an active man and his wife, both of about 

 the same age and weight, the man being rather the heavier and 

 the woman rather the older, who, in carrying out together an 

 experiment on the relative values of vegetable and animal food, 

 both lived for some time on the same kind of diet, and found 

 that nutritive equilibrium was, in the one case and in the other, 

 maintained when 



Proteids. Fats. Carbohydrates. 

 The man consumed daily about 100 70 400 



The wife „ „ ,, 60 67 340 



The most striking difference is in the proteids. 

 § 445. With regard to climate the chief considerations 

 attach to temperature. When the body is exposed to a low 

 temperature the general metabolism of the body is increased 



