90 Fowl Cholera. 



of slaughtered or any parts of the body of affected animals; 

 besides, when healthy fowl drink from the same vessels or from 

 a pond from which infected birds have watered. The infection 

 from cages as well as from the premises may also be dissemin- 

 ated in various ways to neighboring localities where an outbreak 

 may follow. 



The disease is mostly introduced into premises, which have 

 been free from the disease, by the introduction of infected fowls, 

 and less frequently by the sale for food purposes of birds 

 which have been slaughtered while ill. The disease is also very 

 frequently disseminated by poultry shows in which the veteri- 

 nary supervision is very deficient. Further, it may also be 

 disseminated by pigeons which take up the contagion in in- 

 fected premises, become infected themselves and by their in- 

 testinal excrements infect the other birds of the premises 

 (Cagny, Nocard). Finally, the disease may be spread by wild 

 birds, particularly sparrows (Hertel demonstrated virulent 

 bacilli in dermanyssus mites which he took from the body of 

 sick chickens). 



The possibility of the spontaneous occurrence of fowl cholera in 

 localities in which this disease or one of this group has existed is not 

 excluded in view of the general statements made on page 81, but this 

 possibility has not yet been demonstrated by satisfactory observations 

 (according to Gamaleia the intestinal canal of healthy pigeons contains 

 fowl cholera bacteria, but Joest did not succeed in demonstrating them 

 in the intestinal contents of chickens. Ostertag & Ackermann likewise 

 failed to find them in chickens and geese). 



A fluctuation of virulence in the cholera virus is observed under 

 natural conditions as some outbreaks are limited to certain species of 

 fowls, while other species in spite of exposure to the infection fail to 

 contract the disease (for instance, chickens and water fowl are exclu- 

 sively affected). These observations show a still closer accommodation 

 of the virus to the organism of a certain species, as a result of which 

 such accommodated bacteria are strongly virulent for only a certain 

 species of fowl, whereas for another species they are less virulent or 

 non-pathogenic. However, such differences in the virulence are rare 

 and are not constant, and therefore the infections of various species of 

 fowls should not be considered on this basis alone as independent 

 affections. 



Susceptibility. Purebred and water fowl are particularly 

 susceptible to natural infection, whereas the common breed's 

 of fowl show greater resistance. Fowl which have withstood 

 an infection by ingestion a short time before are more suscepti- 

 ble to a second infection. 



Pathogenesis. The bipolar bacilli penetrate the intestines, 

 probably even through the uninjured mucous membrane, into 

 the lymph spaces of the intestinal wall, and soon gain entrance 

 to the blood stream where they multiply with great rapidity 

 and cause the death of the animals. If the entrance of the 

 bacilli takes place through a separation of the continuity of 



