30 REporT OF DEPARTMENT OF ANIMAL HUSBANDRY OF THE 
or composition of the milk. In the former test, during 59 days, 
18.4 Ibs. of fat was formed in the milk which could not have had 
its source in food fat or food protein and could hardly have 
been drawn from the cow’s body. fat as she increased in weight 
33 Ibs. in the same time. In this test Cow 12 in 74 days pro- 
duced 39 lbs. of fat similarly unaccounted for, with a body gain 
of 15 lbs.; and Cow 2, in 4 days, 14 Ibs. These amounts of fat 
must have come from the carbohydrates in the food. 
A lessening of protein supply in the food did not produce a 
corresponding decrease of protein in the milk solids, but caused 
a marked lessening of protein decomposition in the body. 
Calorimeter determinations show that the heat value of urine 
bears no constant relation to its nitrogen content, and also 
prove that the formula used in computing heat energy of urine, 
Nx5.348 Cal., is greatly in error, actual results being from 3 to 
4 times as large as calculated by this formula. The energy 
values of nutrients as given by Rubner,—protein and carbohy- 
drates each 4.1 Cal. and fats 9.3 Cal. appear to be fully high 
enough for herbivora, even when the loss due to escape of 
unoxidized gases, methane chiefly, is not considered. 
Over 49 per ct. of the available energy value of the rations 
was used for maintenance, over 30 per ct. reappeared in the 
milk solids, leaving a balance of from one-fifth to one-fourth of 
the ration. The logical conclusion is that this balance, in part 
at least, sustains the work of milk secretion. 
INTRODUCTION. 
Bulletin No. 132 of the New York Agricultural Experiment 
Station presented the results of an experiment to determine the 
sources of milk fat as related to the food supply. The main con- 
clusion therein stated was that milk fat can be formed in part, 
at least, from carbohydrates, the data of the experiment point- 
ing to this conclusion in a most convincing way. It was felt, 
however, that so important a generalization, if correct, should 
be supported by results secured with more than one animal. 
An opportunity was desired also for enlarging the scope of the 
observations. Experiments have been conducted, therefore, 
