272 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



How Do the Tubercle Bacilli Leave the Body of the Diseased 

 Animal? In a number of ways, depending upon the location of 

 the tubercular nodules. These masses gradually undergo softening 

 and finally break, discharging their contents into the air passages 

 of the lungs and into the milk ducts. The bacteria may thus be 

 thrown off the body in the material coughed up from the lungs, 

 which is, in part, expelled from the mouth, but the larger part is 

 swallowed and the bacteria leave the body in the manure. They are 

 also thrown off in the milk, and in the discharges from the uterus 

 and in the urine. 



How Do the Bacteria Enter the Body of a Healthy Animal? 

 The manure of tuberculous cows gradually undergoes drying and 

 is finally broken into small particles which find their way into the 

 air and are thus breathed in by other cattle. This inhaled dust 

 lodges in the nasal passages and throat, and the tubercle bacilli 

 pass into the glands of the neck and into the lungs. Some of the 

 tubercle organisms are swallowed and finding their way through 

 the intestinal wall, pass into the lymph glands and thus are intro- 

 duced into the circulation. 



Where infected milk is fed to cattle and hogs, the tubercle 

 bacilli penetrate the walls of the throat and intestine and are de- 

 posited in the lymph glands and lungs; hence, these parts are fre- 

 quently diseased. Tuberculous material ejected from the mouth 

 in coughing or drooling is spread in the manger, which surface 

 may be licked by another animal. This direct means of infection 

 is now believed to be a most important way of spreading tuberculo- 

 sis, possibly more so than dust. Hogs running after tuberculous 

 cattle in feeding lots become infected from the manure. 



What Is Open Tuberculosis? When the disease is present in 

 organs that open to the exterior of the body such as the lungs, kid- 

 neys, uterus, and udder. 



What Is Closed Tuberculosis? When the disease is present 

 in parts of the body that have no exterior opening. An animal 

 with closed tuberculosis is not a source of danger to man or other 

 animals since no tubercle bacilli can leave the body. An animal 

 with open tuberculosis is a constant source of danger because the 

 organisms are given off more or less constantly. 



Does Closed Tuberculosis Change to Open? Almost always 

 the disease spreads from the lymph glands to lungs, etc., and then 

 the animal becomes an active means of spreading tubercle bacilli. 

 No one can tell when this may occur, so every tubercular animal 

 must be looked upon as a source of infection and should be re- 

 moved from the herd. 



Is Tuberculous Inherited? But rarely, only when the re- 

 productive organs are diseased. Ordinarily, the disease is con- 

 tracted subsequent to birth. 



How Is the Disease Introduced Into the Herd? 1. By the 

 purchase of diseased animals. 2. By feeding mixed factory by- 

 products, such as raw, creamery skim milk and whey. 3. By di- 

 rect contact with an affected animal. 



