ECONOMY OF HUMAN DIET. 159 
milk 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 i 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 When these are withdrawn for any 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 
, 
