128 Diseases of Poultry 



ported, while encouraging, are too few to allow of definite 

 conclusions. 



Methods of Contagion. — The spread of tuberculosis from 

 fowl to fowl takes place only when the living bacteria are 

 transferred from the diseased to the healthy birds. From 

 the fact that tuberculosis lesions are most commonly found in 

 the internal organs of the digestive system we may conclude 

 that the bacteria usually enter the body along with the food. 

 Examination of the tubercles situated along the intestine 

 shows that in many cases these communicate directly with 

 the interior of the digestive tract. These are constantly 

 emptying enormous numbers of bacteria which are carried to 

 the outside by the feces of the bird. Without doubt the 

 droppings of tuberculous fowls are the most important factor 

 in the spread of this disease. This is especially true when in 

 addition the birds are fed upon ground which is partly 

 covered with these droppings. Besides, the infectious 

 material may very easily be carried by the feet and thus 

 mixed with the food. 



Ward states that there is no evidence to indicate that 

 tuberculosis is spread through the egg. He cites in support 

 of this first the fact that badly diseased birds do not lay, and 

 second the absence of tuberculosis among young stock. 

 Other authors, however, have collected statistics which 

 indicate that even birds badly diseased with tuberculosis 

 may continue to lay quite steadily. 



Koch and Rabinowitsch also make the following statement 

 (p. 431) : "The possibility of the congenital origin of tuber- 

 culosis of fowls through the infection of the fertilized egg with 

 bird tuberculosis is shown by our results. It is also demon- 

 strated by our inoculation experiments on eggs." Further 

 they have given experimental proof of the transfer of tlie 

 bacteria of mammalian tuberculosis from the inoculated egg 

 to the chick. 



