
New YcrK AGRICULTURAL EXPERIMENT STATION. 269 
. Prices of foods used. 
. Cost of food eaten. 
Amount of milk produced. 
. Food-cost of one quart and one pound of milk. 
. Amount of milk-solids produced. 
. Per cent. of solids in milk. 
. Cost of one pound of milk solids. 
10. Money value of milk produced. 
11. Profit derived from selling milk. 
12. Production of milk for manufacture of condensed milk. 
13. General summary. 
1. Unir or Time Aporrep ror ComPARISON. 
Any comparison of individuals or breeds, based upon a few 
weeks or even months, must necessarily be incomplete, imperfect 
and more or less misleading, because our work has shown that 
the influence of the advance of lactation is very marked upon the 
character and yield of milk. We have, therefore, adopted as 
our unit of comparison a period of lactation, and have farther 
defined a period of lactation in this investigation, to consist of 
the first ten months of lactation. Work here and elsewhere fully 
justifies us in fixing upon this arbitrary limit. While some 
animals are more presistent than others in their milk production, 
this quality of persistence is an individual peculiarity rather than 
a breed characteristic, so far as we can yet learn ; and, moreover, 
this quality is dependent upon several conditions and is, to some 
extent, under the control of the dairyman. Some of our animals 
have, in one period of lactation, continued their profitable milk 
production considerably beyond 10 months, and the same 
animals, in the succeeding period of lactation, have ceased to 
produce milk soon after or even before the expiration of 10 
months. Taking the practice of our best dairymen and our own 
experience, we find that 10 months represent very closely the 
average duration of one period of lactation. 
