290 Diseases of Poultry 



the reasons that incubator chicks suffer more from this 

 disease than hen hatched chicks. In the incubator there 

 are eggs from a large number of different hens. There is a 

 great probabihty that one of the mothers may be a bacillus 



Fig. 61. — An ovary from a hen infected with B. pullorum, showing the 

 degenerating and discolored ova. (After Rettger, Kirkpatrick and 

 Jones.) 



carrier and one such infected chick may spread the disease 

 to all the others. With a hen there is much less chance 

 that any of the eggs she broods comes from an infected 

 bird. Hence, while some broods will be infected, others 

 will not and one easily gains the impression that hen hatched 

 chicks are less susceptible. This point will be discussed in 

 connection with prevention (p. 299). 



