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and is precisely of the same composition as flesh. It is, 
therefore, the true nutritive substance in milk, being the one 
from which all the organised tissue of young animals is 
formed. In milk it is probably in the best possible form 
for digestion, being suitable for nearly all stomachs, even 
those of the most tender age ; but when dried, and partly 
decomposed, as we often find it in the form of cheese, 
although still of the same composition and adapted to the 
same purpose, it is not so easily dissolved and assimilated. 
The amount of this valuable nutritive principle in milk is 
found to vary considerably, and to depend, in a great 
measure, on the quality of the food consumed. The more 
nitrogen this food contains, the greater will be the per 
centage of caseine in the milk. 
There are several instances recorded of grass being so 
poor that animals consuming it could not afford to secrete 
any caseine, in consequence of the whole of the nitrogen 
compounds being required for the ordinary vital processes. 
This is stated to have been particularly the case in certain 
cheese farms in the south, where it was found quite im- 
possible to produce cheese until such ingredients as had 
been extracted from the soil had again been restored in 
manure, and, thereby, put it in a position to grow rich 
food again. The ingredients found most useful in re- 
generating this exhausted soil were bones. They supplied 
two of the most essential constituents of milk, namely, 
nitrogen and phosphorus, and, undoubtedly, contributed 
mainly to its normal production. 
In addition to the sugar, fat, and caseine, before men- 
tioned, we find in the serous part of milk considerable 
quantities of phosphates, chlorides, and other salts of potash, 
soda, lime, and magnesia ; in fact, every element which has 
yet been detected as a normal constituent of the human body 
is found here in sufficient quantity and in the best possible 
