528 BIOLOGY AND HUMAN LIFE 



one of the states it was found that about a fourth of the cows 

 yielded so little milk that they did not pay for their keep, while 

 another fourth barely paid for their keep but left no profit to 

 their owners. Some cows produce from four to six times as 

 much milk as others for the same amount of care and feed. 

 Some hens produce from two to three times as many eggs per 

 year as others for the same amount of attention and feeding. 

 The bantam fowl, which is similar to the ancestor of all our 

 modern poultry, laid perhaps from twenty to thirty eggs a year. 

 The best breeds of today have produced hens with a steady 

 yield of over two hundred eggs, with record-breakers of over 

 three hundred eggs. 



For certain purposes the amount of fat, which is converted 

 into butter, may be of more importance than the total yield of 

 milk. Through the use of the Babcock test, which was invented 

 by a professor at the University of Wisconsin and donated by 

 him to the public, it is possible for the dairyman to determine 

 very quickly what percentage of fat there is in a sample of milk. 

 In this way he can keep track of what each cow in the herd is 

 doing from day to day. This has been of substantial help in 

 selecting and breeding for high fat production. 



383. Practical theory. Everybody knows that by practice you 

 can improve your form and your performance in athletics. The 

 same is true of penmanship or of playing the piano. Moreover, 

 the principle of improvement through practice or training 

 applies also to other living things. The people who are rais- 

 ing horses, for example, will tell you that training stables and 

 running tracks are necessary parts of the equipment. If we 

 are going to raise fast horses, one of the things to do is to use 

 as parents animals with a record for fast running or trotting. 

 We should also like to get animals whose ancestors have good 

 records. To a person who is going to buy a high-bred horse the 

 pedigree is just as important as a medical certificate. Finally, 

 we should want to try out our young horses to find out just how 

 fast they are. Now one of the questions that often comes up in 



