CHAP. iv. MILK-PRODUCING CAPACITY. 295 



weather, irregular feeding, brutal usage, fast driving, the mad rushing 

 about provoked by the attacks of the ox warble fly, and a variety of 

 other causes, are bound to exert an influence upon the nerves, the effects 

 of which will be unerringly recorded in the milk-pail. 



The familiar comparison of a cow to a steam-engine is obviously 

 hardly a fair one. Fuel is supplied to the engine, and work is got out 

 of it ; the cow receives food and yields milk ; and if the engine be 

 debited with fuel and the cow with food, and the former be credited 

 with work and the latter with milk, this is about as far as the compari- 

 son can safely be carried. The intimate and essential relation which is 

 set up between the food of the cow and the structure and composition 

 of the animal is of an order vastly superior to that which exists between 

 the fuel of the engine and the inanimate parts which are set in motion, 

 without undergoing any necessary internal change, as a result of the 

 oxidation of that fuel. In estimating the efficiency of a steam-engine, it 

 is quite sufficient to compare the power theoretically deducible from the 

 complete oxidation of the fuel with that exerted at the driving point 

 on the resistance to be overcome ; the difference between the two, shows 

 the loss due to friction and other causes. But, as Sir J. B. Laweshas 

 pointed out, in estimating the milk-producing capacity of a cow, as 

 shown by comparing the amount of food consumed with the quantity 

 of milk yielded, the live weight of the animal is an important element 

 to be considered, particularly in cases wherein the performances of 

 different cows have to be compared. Were the cow a rigid machine 

 like the steam-engine, and were her milk-producing work effected 

 simply by her mechanically receiving food at one place and discharging 

 milk at another, her weight then would be a matter of secondary and 

 trivial importance. But it is obvious that in the cow not only the 

 absolute live weight, but the percentage increase during lactation, 

 should enter as factors into any problem concerned with estimating 

 and comparing the milk- yielding capacities of different animals. 



CHAPTER V. 



OF THE MANAGEMENT OF MILK AND CREAM, AND THE MAKING AND 

 PRESERVATION OF BUTTER. 



""II /TILK is an opaque fluid secreted by the mammary glands of the 

 j.V_L females of animals belonging to the class Mammalia, and 

 adapted to the nourishment of their young. It is of a specific gravity 

 somewhat greater than that of distilled water." 



The average composition of the milk of the cow may be stated to 

 be: 



