14 MASS. EXPERIMENT STATION BULLETIN 295 



Of the 55 vaccinated birds in Group 2, 9 contracted the disease after the usual 

 incubation period for infectious laryngotracheitis in chickens, and of these 1 was 

 killed as a result of cannibalism, 5 died naturally, and 3 recovered. When tested 

 intratracheally for immunity, the 50 vaccinated birds living were found to be 

 immune, but the 16 controls contracted the disease from which 12 died and 4 

 recovered. The surviving chickens were held for thirty-three days and appeared 

 to be developing normally. 



At necropsy 9 vaccinated chickens and 10 controls showed lesions of coccidiosis, 

 and the mortality in both the vaccinated and control groups was confined almost 

 entirely to the birds suffering from this complication. This experiment indicates 

 that birds having chronic coccidiosis are not good risks for bursal vaccination 

 with infectious laryngotracheitis virus. 



In Group 3, 31 of the vaccinated birds were immune and 8 contracted the dis- 

 ease, of which 6 died and 2 recovered. All of the controls developed infectious 

 laryngotracheitis and 21 died while 18 recovered. Lesions of coccidiosis were 

 evident at necropsy in the 8 vaccinated birds showing symptoms of infectious 

 laryngotracheitis and 11 of the controls. Once more the fact was forced upon 

 the investigator that birds weakened by coccidiosis are not good subjects for treat- 

 ment by this method. 



Three days after vaccination two of the birds in Group 4 showed clinical symp- 

 toms of infectious laryngotracheitis and died. A pullet in which the cloaca be- 

 came infected as well as the bursa, died of cannibalism. Of the 62 birds vacci- 

 nated, 59 did not show any symptoms of disease. All of the controls contracted 

 infectious laryngotracheitis and six died, while four recovered. 



Traumatic Cysts 



Four of the vaccinated birds, one pullet and three cockerels, had traumatic 

 cysts in the bursa of Fabricius similar to those shown in the photograph. The 

 cysts looked like tapioca embedded in the mucous membrane, from which they 

 readily shelled out, leaving small cavities. When placed in cold water the cysts 

 swelled up and burst, liberating a sticky gelatinous mass, which gradually went 

 into solution, while the covering membrane remained broken but insoluble in 

 water. The gelatinous mass was precipitated from the solution by the addition of 

 a few drops of 1 per cent acetic acid or alcohol and redissolved in 20 per cent NaOH 

 solution, but it was not redissolved by an excess of acid. The covering membranes 

 were not soluble in any of the reagents used. These tests indicate that the trau- 

 matic cysts consist largely of mucous. 



The significance of these cysts is not fully realized at present. The vaccination 

 must have had something to do with them for they have not been found in un- 

 vaccinated birds. 



The Duration of Immunity 



Fifty-six chickens from Group 4, immune to infectious laryngotracheitis at the 

 time of placing in a colony house, were kept for ten months for studies on the 

 duration of immunity. One of the cockerels died of avian paralysis before the 

 tests were commenced. However, five months after vaccination 55 of the birds 

 were inoculated intratracheally with infectious laryngotracheitis virus, and 6 of 

 them came down with clinical infectious laryngotracheitis. Three of the infected 

 birds died, three recovererl, five developed laryngotracheal rales, and two proved 

 to be chronic carriers. None of the 52 living birds were found to be harboring the 



