668 MODIFICATION OF DIET. [Book ii. 



owing 1 to a regulative action of the nervous system, § 428. We 

 might infer from this that more food is necessary in cold cli- 

 mates ; and, since the increase in the metabolism appears to man- 

 ifest 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 con- 

 stant 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 perspiration 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 fur- 

 ther be expected to increase the fats rather than the carbohy- 

 drates 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 carbohydrates 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 mat- 

 ter, 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 metabolism provoked by cold bears exclu- 

 sively on carbon constituents is so uncertain that it may be 

 doubted whether any change in the normal diet, beyond some 

 increase in the whole, should be made to meet a cold climate. 

 Similar reasons would lead one to infer that man in the warmer 

 climate would maintain on the whole the same normal diet, the 

 only change perhaps being to increase it slightly, possibly 

 throwing the increase chiefly on the carbohydrates with the 

 special view of furthering perspiration. 



§ 446. A special diet for the purpose of fattening, that is 

 to say for the accumulation of adipose tissue out of proportion 

 to the rest of the body, is not needed in the case of man. The 

 power to store up fat in adipose tissue is much more dependent 

 on certain inborn qualities of the organism which we cannot at 



