VARIATION BY FOOD. 
237 
of fish, and then it has the carnivorous stomach; the 
other six months it feeds on grain, and develops 
granivorous lining. Similar experiments have been 
made on pigeons, with the result that the lining of 
the stomach became carnivorous when the bird was 
fed on fiesh, and granivorous when fed on grain. 
These investigations prove that the stomach changes 
its character in accordance with the work it has to 
perform. 
It is claimed that besides determining the structure 
of the stomach, the character of the food also has an 
effect on the length of the intestines. Men in training 
for physical strength know well what food is necessary 
to give them vigor and endurance. Alcoholic liquors 
weaken the constitution, change the color of the skin, 
and cause enlargement of the sebaceous glands, par¬ 
ticularly on the nose. 
It is evident, then, that the supply and character 
of food produce variation. The gardener and stock- 
raiser make good use of this fact, with the assistance of 
selection, in producing new varieties. Food changes 
not only the size but every part of the animal or vege¬ 
table structure. In plants and fiowers the charac¬ 
ter of the tissues, the form of the leaves, the roots, and 
even the fiavor, are affected by it. The mignonette, 
so odorous in rich ground, is destitute of fragrance 
when grown in a sandy soil. In animals the skin, 
the muscles, the secretive tissues, the bones, and the 
brain itself, are modified by food. 
What determines the limits of the stature of ani¬ 
mals and plants ? Why does not the hen continue to 
