158 
POPULAR SCIENCE REVIEW. 
individual requires not only food in an increasing ratio_, but 
also blood and beat-producing elements in dijfferent propor- 
tions^ according to bis age and weight. 
To Hcmhner is to be attributed tbe great merit of having in 
a practical manner caused farmers to understand tbe necessity 
of a just proportion of these two classes of substances in tbe 
nutrition of animals ; a circumstance to which I had called 
attention in my Familiar Letters on Chemistry.-’^ By the 
admirable investigation of Henneherg, Stolimann, Kno^j, Arendt, 
Baehr, Pincus, and others who followed in his steps, the 
foundation of a scientific doctrine of nutrition has been laid. 
The farmer is enabled by it to supply the failing milk or hay — 
the universal food for young and grown animals — by the coiTect 
mixture of other provender which his field produces, oat or 
rye straw with turnips, roots, potatoes, rapemeal, pease, and 
beans, as the case may be. By following strictly the law of 
nutrition, many farmers have succeeded in producing milk 
and flesh much cheaper than before, often indeed at half 
the cost. 
The above-mentioned researches have proved that when the 
two elements of food have been given in proper relative pro- 
portions, befitting the wants of the individual, the result of 
the two is a maximum of the nutritious effect belonging to 
each. 
A smaller proportion of heat-producing matter than is wanted 
may be replaced in the food by a certain amount of blood- 
forming elements, but that excess over the required quantity 
loses its nutritive value : that is, its power to increase the 
weight of the body, or of forming flesh. The heat-forming 
substances are incapable of forming blood or flesh ; an excess 
of them in the food therefore produces no effect. It is pre- 
supposed that the individual receives as much food as the 
inclination or appetite demands. 
If we admit that a boy, merely to keep up his weight, re- 
quires daily half-an-ounce of blood and flesh-producing matter, 
we shall see that he would receive this from a potato diet, if 
he were able to consume daily I-| lb. (24 ounces) of steamed 
potatoes. For the increase of the muscular substance in his 
body, he would have to take a still larger quantit}^. 
Potatoes contain, for every one part of blood-forming matter, 
from 9 to 10 — let us say 10 parts of heat-producing sub- 
stance (starch). In 24 ounces of steamed potatoes are 5 ounces 
of starch, of which only 2-| are employed in the body for the 
production of heat. The remaining 2^ ounces burthen the 
intestines, and pass away without doing any good. 
In 5 ounces of pease is 1 ounce of blood-forming substance 
(as much as in 48 ounces of steamed potatoes), besides 2^ 
