IMMUNOLOGY OF LARYNGOTRACHEITIS 



17 



Virus X, Table 12, was not very satisfactory because it was lost twice, once in 

 chickens V-1212 and V-1213, and again in chickens V-1233 and V-1234. Virus 

 Y, Table 13, was cultivated continuously in the bursa of Fabricius for 58 days 

 without loss of virulence, or change in immunizing properties. The bacterial 

 flora was different than in viruses from the respiratory tract. The bacteria were 

 of intestinal origin and did not influence the results in vaccinations, but further 

 study is needed to clear up this point. This study was not continued further at 

 this time because no advantage was obtained in cultivating the virus exclusively 

 in the bursa of Fabricius, since a better check on the virulence was maintained 

 when the chickens were inoculated intratracheally. 



However, in selecting a virus for vaccine in the future, virus Y will be chosen 

 rather than virus X, because of its uniform results in this experiment. 



