382 now TO make the farm pay. 



food, lias been fully investigated, so that we know what constit- 

 uents produL'c fat, what are heat, and what are flesli producing, 

 what <^oes to build up the bony structure, and what enters into 

 th.e muscular tissues; but while there is much of practical 

 interest in these investigations, we are not to overlook the fact 

 that, in actual practice, we have to deal with living organiza- 

 tions, and that the most conflicting variety of circumstances 

 often comes in to modify the results which theory would lead us 

 to expect. Instead of the test-tubes and retorts of the labora- 

 tory, in which a certain number of materials, under certain cir- 

 cumstances, will invariably combine and form a certain substance, 

 we now have the living animal, with its fine adjustment of ner- 

 vous and muscular organizations, and we find that our results 

 depend upon physiological peculiarities, upon likes and dislikes, 

 upon circumstances over which we have not always a full control. 

 Food relished one day will be rejected another. That which 

 gives satisfactory results at one time will utterly fail at another. 

 Under precisely the same conditions of shelter, food, and man- 

 agement, so far as we can tell, the yield of milk will vary in 

 the same cow ; and while one cow thrives on one kind of food, 

 another will not. Let the system of management remain the 

 same, and the quality of milk of the same cow will often vary, 

 be rich and buttery at one time, and watery or cheesy at 

 another. 



Many of those changes and variations, which introduce an 

 element of uncertainty into our calculations are due to hidden 

 causes, but there are others which we know more about, and 

 which have an important influence over the nutritive value of 

 food. Bad air, or want of ventilation in the stall, will reduce 

 not only the quantity, but the value of milk. Fright or worry- 

 ing by dogs, or fast driving, the irritation caused by flies in the 

 pasture, any thing in fact, which disturbs the quiet of the ani- 



