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NITROGENOUS FEEDING STUFFS. 89 
been lately indicated by a very interesting experiment con- 
ducted under the direction of Prof. W. H. Jordan at the New 
York State Experiment Station, that milk fat can be made 
from the carbohydrates of the food.* 
Just how the different ingredients of the milk are formed 
and just what ingredients of the food or the body are used for 
their production, physiological science has not yet definitely 
told, although a great deal of valuable information has accu- 
mulated. The same is true regarding the formation of other 
materials in the body and the ways in which the different 
ingredients of the food are used for the purpose. But at the 
same time the amount of exact information we now have is 
very considerable. 
One thing which feeding experiments and practical experi- 
ence in feeding are bringing out very forcibly is the importance 
of fitting the food to the special needs of the animal for main- 
tenance and for the kind of production demanded of it. For 
instance, a cow giving milk needs the different nutrients of her 
food in the proportion which will best serve for the mainte-: 
nance of her body and for the making of milk. Her body may 
be regarded as a machine for manufacturing milk. Itisa very 
delicate machine and requires a great deal to keep it running; 
that is, for maintenance, whether it is actually producing or 
not. For the manufacture of milk it needs raw material. This 
raw material, which is to be made into milk, is the same as the 
material used to keep the machine in repair and for fuel to 
keep it in motion. But this raw material consists of different 
kinds of ingredients—protein, fats, carbohydrates, and others, 
and if we are to get the largest and best product with the least 
costly raw material, and the least injury to the machine, the 
proportions must be fitted to the demands. 
In thus fitting the food to the requirements of the cow it is 
necessary to have enough protein, because it‘has a Special 
work to do for which no other of the nutrients will suffice. 
If we have too little of the fuel ingredients we can make up 
the deficiency with extra protein, but if the protein for build- 
ing and repair and the production of the albuminoids of the 
milk is lacking no amount of other ingredients will take its 
place. - 

* New York State Experiment Station, Bulletin No. 132, On the Source of Milk Fat. 
