172 MASS. EXPERIMENT STATION BULLETIN 278 



to freeze and fail to reach all of the places intended. In addition, colds and 

 roup are likely to appear as complicating factors due to increased draughts and 

 dampness. Usually the best time to clean up after an outbreak of infectious 

 laryngotracheitis is in the summer. All litter should first be removed from the 

 house and burned. Then the house should be thoroughly washed with hot water 

 and disinfected with one of the "Permitted Disinfectants. "^ The liquid should 

 be sprayed with a force pump, or rubbed into all cracks with a good stiff broom. 

 After standing for a week with doors and windows open to admit light and air, 

 the premises should be free of infectious laryngotracheitis. 



Summary 



L Sparrows and mice are not important mechanical carriers of infectious 

 laryngotracheitis. 



2. Ten pigeons inoculated intratracheally with virulent strains of infectious 

 laryngotracheitis failed to contract the disease, or to carry the virus in their 

 tracheas for any great length of time. 



3. Man may serve as a mechanical carrier of the virus if he handles birds 

 in the acute stages of the disease and directly picks up susceptible chickens, 

 pullets, or cockerels. 



4. Acute cases eliminate virus as long as they live, up to 10 or 15 days, or 

 until they show no visible symptoms of the disease. 



5. Fourteen chronic carriers out of 504 birds tested eliminated virus for 

 indefinite periods. 



6. The number of chronic carriers in a flock surviving an attack of infectious 

 laryngotracheitis depends upon the size of the flock and the virulence of the 

 virus. 



7. If the birds used for breechug pui-poses have had infectious laryngotra- 

 cheitis and the pullets and cockerels have remained free of it, the two flocks 

 should be kept separate in order to break the cycle of infection and get rid of 

 the disease. 



8. The respiratory tract seems to be the most important channel of infection. 



9. Usually the best time to clean up and disinfect after an outbreak of 

 infectious laryngotracheitis is in the summer. 



10. It should be borne in mind that the control measures suggested in this 

 bulletin are based upon a laboratory study of infectious laryngotracheitis, and it 

 is too much to expect that they will meet all situations arising in poultry practice 

 without some adaptation or modification. 



2 A list of the permitted disinfectants may be prociirfd by ;ippiic:ition to tlie Inited .States De- 

 partment of Agriculture, Washington, D. C. 



