12 MASS. EXPERIMENT STATION BULLETIN 295 



manner. Desiccated virus was groiniil up in a sterile mortar with sufficient sterile 

 saline solution to make a thin paste. A pinch of cotton was twisted on the end of a 

 wooden applicator to make a swab that would easily pass through the opening 

 leading into the bursa of Fabricius. The swab was dipped into the paste, and 

 gently pushed through the bursal orifice of each bird and the mucous membrane 

 carefully swabbed, taking care to get between the folds. Beginning the third day 

 after inoculation, a swab was inserted into the bursa of each bird and some of tha 

 exudate removed and re-inoculated into the tracheas of chickens which had never 

 been exposed to infectious laryngotracheitis. The results of this experiment are 

 reported in Table 9. 



Table 9. — The Number of D.\ys the Virus Was Recovered from the Bursa 



In this table the unimmunized birds refer to the 12 chickens which had never 

 been exposed to infectious laryngotracheitis until they were vaccinated in the 

 bursa of Fabricius, and the immune controls are the ones which had been previous- 

 ly immunized by the intravenous method. This experiment indicates that the 

 bursa was infected in the unimmunized birds and was not infected in the immune 

 controls. Evidence of this was further demonstrated on physical examination of 

 the cloaca and the opening into the bursal orifice. On the third day after vaccina- 

 tion, the bursal orifice and sometimes the cloaca were inflamed and swollen in 

 the unvaccinated birds, while these parts in the immune controls remained practi- 

 cally normal. 



Also this experiment indicates that the virus was retained in the bursa of Fabri- 

 cius of the unimmunized birds for five days after vaccination, before it began to 

 disappear, and it was demonstrated in some of the birds up to the ninth day. The 

 virus in the bursa of the immune controls apparently began to deteriorate at once 

 and could not be demonstrated four days after inoculation. 



Two weeks after all visible inflammation and swelling of the bursal orifice had 

 ceased, the chickens were inoculated intratracheally with infectious laryngotrache- 

 itis virus and were found to be immune. Four controls inoculated at the same 

 time contracted the disease and three died. 



After it had been established that the bursa of Fabricius could be infected with 

 the virus of infectious laryngotracheitis, and that the infection was apparently 

 of sufficient duration to stimulate the production of immune bodies which reached 

 the mucous membrane of the trachea, it was decided to immunize birds on a 

 comparatively large scale, under laboratory conditions, and to determine the 

 duration of immunity established by this method more fully, as well as to study 

 any other complications which might arise. No special refinements were made in the 

 preparation of the vaccine, e.xcept that the viruses used had been prepared by the 

 Swift method (Gibbs, 1933a), and had killed chickens one month old in a week. 

 This arbitrary standard seemed to be necessary, because it was observed in pre- 

 liminary experiments that the bursa of Fabricius was not as easily infected as the 

 larynx and trachea, so that any virus of diminished virulence might not produce 



