CHAP, v.] NUTRITION. 883 



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. 



555. 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 owing to a 

 regulative action of the nervous system, 534. We might infer 

 from this that more food is necessary in cold climates ; and, since 

 the increase in the metabolism appears to manifest itself chiefly 

 in a greater discharge of carbonic acid and therefore to be 

 especially a carbon metabolism, we might infer that the carbon 

 elements of food should be especially increased. When the body 

 is exposed to high temperatures the same reflex mechanism tends 

 to lower the metabolism; but the effects in this direction are 

 much less clear than those of cold, and soon reach their limits ; 

 the bodily temperature is maintained constant under the influence 

 of surrounding warmth not so much by diminished production 

 as by increased loss. We may infer from this that in warm 

 climates not less but if anything rather more food than in 

 temperate climates is necessary in order to supply the per- 

 spiration needed for the greater evaporation and discharge of 

 heat by the skin. 



In both cold and warm climates however man trusts much 

 more to variations in his clothings and immediate surroundings to 

 protect him against cold or to guard him from heat than to any 

 marked variations in his normal diet. In the former he may 

 perhaps be expected to eat somewhat more, since, in spite of 

 wrappings, his skin still feels in part the cold, and thus the 

 nervous mechanism for the increase of metabolism is to a certain 

 extent set to work. And since the metabolism thus increased 

 appears to affect especially the carbon of the body, he may further 

 be expected to increase the fats rather than the carbohydrates of 

 his food seeing that the former supply him with the most energy 

 for their weight. But it is very doubtful whether what he might 

 thus be expected to gain over a corresponding increase in carbo- 

 hydrates is not more than counterbalanced by the increased labour 

 of digestion; and the habits of the dwellers in arctic climates 

 cannot safely be taken as guides in this matter, for their reputed 

 love of fat is probably the result of that being their most available 

 form of carbon. Indeed the evidence that the increase of meta- 

 bolism provoked by cold bears exclusively on carbon constituents 



