340 ELEMENTS OF AGRICULTURE 



discovered. This is by the tuberculin test. The tempera- 

 ture of the animal is taken at intervals for a day. Tuber- 

 culin is then injected under the skin. If the animal 

 has tuberculosis, the temperature will rise a few degrees 

 during the following day. A number of cautions have to 

 be observed in making the test and interpreting results. 

 The work should be done by a good veterinarian, or by 

 an exceedingly careful and well-trained farmer. 



Some persons have feared that tuberculin would pro- 

 duce the disease. It is prepared by allowing tubercle 

 bacteria to grow in a liquid usually containing beef extract. 

 Before it is used, it is twice heated and twice filtered, 

 any one of the four operations being sufficient to remove 

 or kill all germs. No injury comes from its intelligent use. 



It is sometimes desirable to keep diseased animals for 

 breeding purposes. The calves are removed as soon as 

 born and all milk is pasteurized before being fed. In this 

 way a healthy herd has often been developed from a dis- 

 eased one. The two herds must be kept separate at all 

 times. If a large part of a herd is diseased, the animals 

 that do not react are not removed, as they are likely to 

 develop the disease later. This method of developing a 

 sound herd is named the Bang method, after its originator. 



302. Milk Fever. One of the serious diseases of dairy 

 cows is milk fever. It attacks the best animals. Formerly, 

 it was the great obstacle in the way of developing superior 

 cows. It has been found that the disease can be easily 

 cured if air is pumped into the teats so as to distend 

 the udder. After each quarter is rilled, the teat is tied 

 so as to hold the air in it. The only danger is that bacteria 

 may be introduced into the udder. The apparatus must 



