150 THE HORSE IN HEALTH AND DISEASE 



vitality of the stock. Breeding from immature or diseased animals 

 is the main cause of inherited weaknesses. The evil effects are 

 seen in the offspring of inbred parents and those of too young or 

 pampered mares. The foals may be of normal size, but lack 

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

 life. By breeding only from sound, mature stock diseases and 

 weaknesses of this nature can be avoided. 



The elimination of agents which spread infection is necessary 

 if diseases are to be effectively controlled. Here consideration 

 should be given to dogs, birds, and all animals coming from infected 

 places, whether they themselves are sick or apparently healthy; 

 hay and grain from quarantined areas; water from public drinking 

 troughs and other contaminated sources; stock cars, pens, and 

 shows. 



Disinfection is the process of destroying disease germs by 

 means of heat, cold, chemical substances, or fumigation. It is the 

 chief weapon of the sanitarian in preventing and controlling infec- 

 tious diseases. Disinfection differs from antisepsis in that it has 

 for its object the absolute destruction of micro-organisms instead of 

 simply preventing their growth and development. 



The ideal disinfectant is one which will destroy the germs with- 

 out injury to the object. There is no one agent or method apphc- 

 able in all cases, therefore the conditions must be studied in each 

 case and the most suitable disinfectant selected. In any event, 

 the disinfectant must come in actual contact with the material 

 which is to be disinfected for effective results. 



Heat in the form of fire is the most valuable and reliable disin- 

 fectant. A discussion of its action would be absurd, for all under- 

 stand the manner in which it works. Cold is less effective than 

 •heat as a disinfectant. In the northern states, where the winters 

 are long and rigorous, most disease-producing micro-organisms 

 are unable to survive unless protected in manure piles and other 

 places secluded from frosts. In some outbreaks of infectious dis- 

 eases it has been observed that there is a tendency for them to 

 "die out" in the winter. The action of cold is often accountable 

 for this desirable turn, but too much reliance should not be placed 

 in it, besides the chances of introducing a fresh infection are 

 numerous. 



Chemical disinfectants are most commonly used about the farm 

 because they are easiest to apply. It is impossible to state which 



