196 FIRST PRINCIPLES OF AGRICULTURE. 



The Selection of a Specialty is also important ; for, 

 while a series of products may be made, the adoption of 

 a single line usually results in a greater concentration 

 of energy, and hence a better product. This involves 

 a knowledge of the special characteristics of the differ- 

 ent breeds, and the principles that govern in their selec- 

 tion, management, care, and improvement. 



Testing the Animals. The profits of the dairy are 

 also governed in large measure by the yield and quality 

 of the milk ; hence careful records should be kept of 

 individual animals in these respects. It has already been 

 shown that the yield and quality of the dairy products, 

 cream, butter, and cheese, are measured by the content 

 of butter-fat in the milk ; it is, therefore, of the great- 

 est importance that the content of fat in the milk of 

 each animal should be tested. This may be accurately 

 and rapidly accomplished by what are known as semi- 

 chemical methods ; of these the " Babcock Test," de- 

 vised by Dr. S. M. Babcock of the Wisconsin Experiment 

 Station, furnishes accurate results, and is so simple in 

 operation as to be readily performed by any careful 

 dairyman. 



A careful study of the animals in these respects teaches 

 the dairyman the actual value of each, hence only those 

 which are profitable need be kept. 



Dairy Products and Soil Fertility. The relation 

 of the sale of the various dairy products to soil ex- 

 haustion is frequently disregarded in the selection of 

 specific lines, though it is a matter of some importance. 

 If whole milk is sold, there is removed from the farm 

 for each ton sold an average of twelve pounds of nitro- 



