58 MASS. EXPERIMENT STATION BULLETIN 305 



of virus was used in preparing the vaccine. This virus had been studied in the 

 laboratory several months and was maintained in one-month-old chickens, which 

 had also been reared under laboratory conditions since they were two days old. 

 The chickens for the laboratory studies were all secured from a single poultry- 

 man, and were uniform in size, appearance, and resistance. The virus was not 

 used in the field experiments as vaccine, unless it killed one-month-old chickens 

 in five days. This arbitrary standard was necessary because laboratory tests 

 indicated that any attenuation in the virulence of the virus might produce un- 

 satisfactory vaccine. 



A special technique was devised for restraining the birds and making the inocu- 

 lations. In the field experiments the percentage of takes varied from 80 to 100 

 per cent, depending upon the age of the birds. As far as takes were concerned 

 the most satisfactory results were secured with chickens three and four months 

 of age. This period correlated with the age of greatest susceptibility in chickens 

 inoculated intratracheally with fresh virus. 



Up to the present it has not been definitely proved whether this correlation is 

 real or apparent. Anyway, it was found that the number of successful takes 

 fell ofT proportionally as the chickens were older or younger than three and 

 four months. These variations may have been due to the fact that natural 

 resistance of chickens to vacccination increased with age, while difificulties in in- 

 oculating the bursa of Fabricius and the cloaca increased with the smallness 

 in size. 



The vaccinated birds are being checked for cloacal and laryngotracheal carriers. 

 The results of this part of the experimental study will be reported later. 



Distribution and Epizootiology Studies of Infectious Laryngotracheitis. (C. S. 



Gibbs.) This study is being conducted jointly by the Department of Veterinary 

 Science and County Agents. The object is to make a thorough investigation 

 of the distribution and epizootiology of infectious laryngotracheitis in Massachu- 

 setts. It is hoped that this study will eventually lead to some practical methods 

 of controlling the disease. As yet the information which has come in is meager, 

 although it is sufficient to indicate that the disease is confined largely to the 

 eastern part of the State, and some counties have more of it than others. Factors 

 other than chronic carriers seem to be instrumental in the spread of the disease 

 from endemic centers. Just what these factors are in each locality has not yet 

 been determined. It is impossible to formulate satisfactory control measures 

 until these factors are known and other field studies completed. 



Further Studies on the Desiccation and Preservation of Infectious Laryngo- 

 tracheitis Virus. (C. S. Gibbs.) Recent experiments in this laboratory have 

 shown that the virus of infectious laryngotracheitis may be satisfactorily des- 

 iccated and preserved by filling a properly prepared desiccator with dry air. 

 The air is dried by passing over anhydrous calcium chloride, and through alkaline 

 pyragallol and sulfuric acid. The dry air is drawn into the desiccator by means 

 of an ordinary water pressure pump. 



This method of desiccating and preserving infectious laryngotracheitis virus 

 ofTers no advantage over the modified Swift method, which has been in use in this 

 laboratory for several years, except that a vacuum pump is unnecessary, and the 

 cost of equipment reduced. 



Avian Paralysis or Neurolymphomatosis. (C. S. Gibbs.) An apparent rela- 

 tion of l^mphocytoma to neurolymphomatosis has been demonstrated in a sys- 

 tematic study of malignant growths and paralytic conditions in a flock of known 

 history. In some of the cases under study the pathological cell involved in 



