212 PRINCIPLES OF VETERINARY SCIENCE 



have shown that the germs of tuberculosis may remain alive in 

 cow manure for nearly a year and in water for even a longer time. 

 The germs of anthrax are known to retain their vitality in dry 

 soil for fifteen years. 



The main factors in keeping an animal healthy are a strong 

 constitution, which is inherited from healthy parents; good 

 condition, which is maintained by adequate food, water, air, 

 light, and shelter; protection from injury and disease. These 

 factors have been referred to in previous pages. In addition, 

 when a serious attempt is made to prevent and control disease, 

 attention must be paid to the following important procedures: 



(1) The Selection of Animals for Breeding. — If animals used 

 for breeding purposes are defective, their offspring will inherit 

 weakened constitutions. Breeding from immature, inbred, 

 unsound, or very old animals, either dams or sires, is the main 

 cause of inherited weaknesses. It is a mistake to use for breed- 

 ing purposes animals that show physical weaknesses. The 

 progeny of such animals may be of normal size, but lack vitality 

 and either are born dead, or die during the first few weeks of 

 life. Others lack in development when born and never overcome 

 the handicap. By breeding only from sound, vigorous, mature 

 stock, diseases and weaknesses of this nature can be avoided. 

 Before making a final selection of a pure bred animal for breed- 

 ing purposes, great care should be taken to determine that it 

 meets these requirements. Besides paying careful attention to 

 the selection of animals, the breeder should avoid unnatural 

 forcing and pampering; should look particularly to size, energy, 

 and massive development in the male and to fine quality and 

 maternal characters in the female. Reference should be made to 

 text-books on animal breeding for further information relative to 

 breeding practices. 



(2) The Increase of the Resistive Powers of the Body.— 

 This is a means whereby infectious diseases may be prevented. 

 The process of conferring protection against disease by treatment 

 with either an attenuated form or a sublethal quantity of the 

 infectious agent of the disease or its products is spoken of as 

 "active immunization." Immunization is recommended either 

 when other methods of prevention are impracticable, or when 

 it is desirable to strengthen the body against a specific in- 

 fection. To be of the greatest value it should be employed 



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