20 



HOW THE DISEASE SPREADS. 



Sooner or Liter the tuberculous cow begins to give off the germs of the 

 disease. The germs escape by the mouth and nose, the bowels, in the milk, 

 nnd in discharges from the genital organs. When the germs are being given 

 off in any of these ways, the disease is known as open tuberculosis. 



Germs discharged from the mouth and nose are coughed up from the 

 Inngs and are sprayed over the food in front of the cow or are carried in the 

 air for a time until they fall to the ground. Cows in adjoining stalls may 

 take in these germs in the air they breathe or in the food they eat, and so con- 

 tract the disease. 



Germs discharged from the bowels are mixed with the manure, and may 

 infect cattle and hogs that are allowed to pick over the dung heap. The prac- 

 tice of having hogs and cattle together in the same yard is sure to result in 

 the infection of the hogs, if any of the cattle are affected. The germs in the 

 manure come from matter that is coughed up and swallowed, and in some case's 

 from tuberculosis in the bowels themselves. Manure containing tubercle 

 germs may easily infect the milk. Particles of dried manure may .fall 

 into the milk pail from the skin of a dirty cow or be accidentally flicked off 

 from the tail and fall into the milk. Straining the milk afterwards only 

 lemoves the larger particles. The smaller ones, including the germs, remain 

 in the milk. 



When the udder is tuberculous, the milk contains the germs in vast num- 

 bers. Such milk may look and taste perfectly good, but readily transmits tho 

 disease to young animals. It is very dangerous to children. Hogs and calves 

 are very readily infected by it. 



HOW A HERD IS INFECTED. 



Tuberculosis may be introduced into a healthy herd in a number of ways : 



1. By the purchase of a bull or other animal that is infected with the 

 disease. This animal may be apparently healthy at the time of purchase, but 

 if it contains the germs, the disease may develop and spread to other cattle. 

 ISTew animals should only be bought from a herd that is known to be healthy. 



2. By feeding calves with milk, buttermilk, or whey that has come from 

 tuberculous cows. A farmer may have a healthy herd, Ijut if he brings home 

 skim mil]? from a creamery and feeds it to his calves, he may give them the 

 disease. Such milk should be rendered safe by boiling or pasteurizing it. 



3. By showing cattle at fairs and exhibitions where no proper care is 

 taken to keep out diseased stock, or to disinfect the stables. 



4. By shipping animals in cars that have not been disinfected, as these 

 may have recently carried diseased cattle. 



5. By allowing cattle to graze with diseased ones, or to come in contact 

 with them over fences. 



