LARYNGOTRACHEITIS VACCINATION 13 



little water from the kitchen. With this crude equipment the writer, the owner, 

 and a man hired for the occasion set out to save the chickens on the range from 

 dying of infectious laryngotracheitis. Thirty of the pullets showing marked 

 symptoms of infectious laryngotracheitis were sacrificed to make vaccine, and 

 the 800 chickens on the range were vaccinated in the cloaca and bursa of Fab- 

 ricius. Five days later the flock was examined for takes, with results recorded 

 in Table 6. 



In addition it was estimated at the time the birds were examined for takes that: 



(1) 704 or 88 percent showed takes and no symptoms of disease. 



(2) 64 or 8 percent showed both takes and symptoms of disease. 



(3) 28 or 3.5 percent showed no takes and no symptoms of disease. 



(4) 4 or 0.5 percent showed no takes and symptoms of disease. 



All of the birds recovered and remained free of infectious laryngotracheitis 

 through the year except the four which showed no takes and symptoms of disease. 

 The birds not showing takes were not revaccinated at the time the examination 

 for takes was made and the results were entirely satisfactory to the poultryman. 



Cloacal and Bursal Carriers in Field Experiments 



After the field vaccinations had been completed it was felt that the presence or 

 absence of cloacal and bursal carriers in vaccinated flocks was still unsettled, 

 because the studies hitherto had been limited to one group of 55 birds (Gibbs, 

 1933b) and another group of 30, which may not have been sufficient to give a cor- 

 rect interpretation. So 620 birds from Flock 4 were systematically examined for 

 cloacal and bursal carriers beginning two months after vaccination. This flock 

 was divided into four groups of 155 birds. Each group was swabbed in the cloaca 

 and bursa, and chickens inoculated intratracheally with the exudate until all 

 of the birds had been examined. 



The cloacas and bursas of 560 hens and 40 roosters were found to be free of 

 microorganisms or viruses pathogenic to baby chicks. The chickens inoculated 

 from these hens and roosters remained healthy throughout the experiment. 

 The cloacas and bursas of 20 of the hens may not have been free of microorganisms 

 or viruses, because the chickens inoculated from them developed dyspnea and 

 died of asphyxiation as in infectious laryngotracheitis. After death the larynx 

 and trachea were found plugged with pseudomembrane. Histological studies 

 of the larynx and trachea of the diseased chicks indicated that the inflammation 

 was a desquamative epithelial inflammation. The disease could not be trans- 

 mitted beyond the first group of chickens inoculated directly from the hens. 

 No bacteria other than those occurring normally in the larynx and trachea could 

 be found. The disease was not obtained by swabbing the tracheas of chickens 

 with clean swabs. It occurred in the same proportion in a smaller number of 

 unvaccinated hens. Therefore the disease did not appear to be traumatic or 

 confined to vaccinated birds. The specific cause was not determined, although 

 it occurred quite regular!}' in the same birds, as the following study shows. 



Four groups of chickens were inoculated at different intervals with exudate 

 from 10 vaccinated and 10 unvaccinated birds showing the disease, and from 10 

 vaccinated and 10 unvaccinated birds not showing the disease. Results are 

 shown in Table 7. 



A study of Table 7 shows that the disease was more persistent in the unvac- 

 cinated birds, but evidence was lacking to indicate that vaccination had anything 



