170 ,MAS5>. EXl'EKl.MEN'r S'I'ATIU.N BILLETIN 278 



As soon as the chronic carriers ceased to eliminate virus from the trachea, 

 they were killed, and the internal organs were tested for the presence of virus 

 by direct and indinn-t methods. The virus was not found in any of the internal 

 organs examined; but it should be borne in mind that the total number of car- 

 riers was limited to 14, and that it is difhcult to demonstrate the virus of infec- 

 tious laryngotracheitis in the tissues of birds by laboratory methods, unless it 

 is present in large ([uantities. 



Experiments with Dried Infectious Laryngotracheitis 

 Tissues and Exudates 



The cages used in the experiments with man as a mechanical carrier were 

 disinfected by sul)merging for 12 hours in a tank containing 3 per cent cresol 

 solution, numbered, and returned to the stands. Twenty-four pullets and cock- 

 erels were placed in the cages. For a month the birds in the A cages were fed 

 desiccated diseased tracheal tissues ami exudates, but none of them developed 

 the disease. At the end of the month the birds were inoculated, intratracheally, 

 with tracheal exudate from a jiuUet dying of the disease and all were found to 

 be susceptible. 



The litter in the B cages was thorouglily dusted with some of the same ma- 

 terial that was fed to the birds in the A cages, except that it was ground to a 

 fine powder. All of these pullets and cockerels developed the disease in three to 

 seven days after the first dusting, and six of them died. 



The birds in the C cages were fed powdered infectious laryngotracheitis 

 material in gelatine capsules, but did not take the disease. Later their tracheas 

 were swabbed with powdered tissues and exudates and all of them developed 

 the disease and died. 



These laboratory investigations indicate that the virus is not likely to cause 

 disease in susceptible pullets and cockerels unless it is in some form that will 

 readily attach itself to the nuicous membrane of the respiratory tract. In other 

 words, the channel of infection in laryngotracheitis seems to be the respiratory 

 tract, and it makes little difference whether the virus is moist or dry; for dupli- 

 cate feeding experiments with moist tracheal tissues failed to infect susceptible 

 chickens while the spraying of liquid exudates invariahly produced the disease. 



The Viability of Infectious Laryngotracheitis Virus Under 

 Natural Conditions in a Poultry House 



The preceding investigation indicated that the environment in some poultry 

 liouses might be conducive to the preservation and spread of infectious laryn- 

 gotracheitis, especially in cold weather. An experiment was therefore planned 

 to determine the viability of the virus under these conditions. In this experi- 

 ment small pieces of epithelium, pseudomembrane, and tracheal exudate were 

 scraped from the tracheas of fowls dying of the disease, and placed in serological 

 test tubes which were plugged with cotton. Then the tubes were buried in the 

 litter on the floor of the j)oultry house. Every day during the course of the ex- 

 periment, except Saturday and Sunday, a tube was dug up and the contents 

 examined and us(>d to itioculatc chickens susceptit)l(' to infectious laryngotra- 

 cheitis. 



The results of this experiment indicate th;it the virus was not i)reserved 

 for any great length of time under the conditions in the litter of the poultry 

 house, except during the latter part of .I.nnuary and the first i)art of February 



