ECONOMY OF HUMAN DIET. 159 



or curdled-milk with potatoes ; and the combination of 

 rice and fat, which is the staple of the diet of many Eastern 

 nations. Even the morsel of butter or the bit of cheese 

 which the English labourer eats with his hard-earned bread, 

 are not matters of luxury, but have a positive importance ; 

 and the existence of these tastes and habits shows how by 

 long experience Man has at last learned to adjust the com- 

 position of his food, so as best to maintain the health and 

 vigour of his body. With a difference of requirement comes 

 a difference of tastes. Thus men who are going through a 

 very laborious course of exertion, prefer meat to bread or 

 vegetables, feeling it to be more sustaining to their strength. 

 On the other hand, those who are continuously exposed to 

 the severity of an Arctic winter, eat with relish large masses 

 of fat, on which they would look with disgust under other 

 circumstances. The quantity of work which a man can do, 

 and his power of sustaining extreme cold, both depend in 

 great part, as has now been abundantly proved, upon the 

 adequacy of the sustenance he takes : the demand, in the first 

 case, being for albuminous material to supply the waste of his 

 tissues ; whilst in the second it is for combustive material 

 suitable to generate heat in large measure, a purpose which 

 is far more efficiently answered by oleaginous substances, than 

 by those of a starchy or saccharine nature. Experience fur- 

 ther shows that the healthy condition of the blood of Man 

 can only be maintained by the use of fresh vegetables as part 

 of his ordinary diet. "When these are withdrawn for any 

 length of time, the disease known as Scurvy is certain to 

 appear, unless lemon -juice or some other efficacious anti- 

 scorbutic be employed as a substitute. This is a fact of the 

 utmost importance in provisioning ships for long voyages ; 

 the tendency to scurvy being increased by confinement 

 and insufficient ventilation, and by the exclusive use of salt 

 provisions. 



166. Besides these organic substances, there are certain 

 Mineral ingredients, which may be said to constitute a part 

 of the food of Animals ; being necessary to their support, in 

 the same manner as other mineral substances are necessary to 

 the support of Plants. Of this- kind are common salt, and 

 also phosphorus, sulphur, lime, and iron, either in combina- 

 tion or separate. The uses of Salt are very numerous and 



