6 MASS. EXPERIMENT STATION BULLETIN 295 



Table 4. — Tests of the Duration of Immunity Imparted to Chickens by 

 Intermittent Intravenous Inoculations with Small Doses of Virus 



Because of the difficulties in administration, uncertainty of results, and expense, 

 the intravenous immunization of chickens against infectious laryngotracheitis 

 may never be practical under field conditions; yet it has served to demonstrate 

 that chickens may be immunized by this method in the laboratory. 



Subcutaneous Inoculation 



Since it was found that chickens could be immunized by intravenous inocula- 

 tions of small doses of virus over a period of 28 days, attempts were made to 

 immunize chickens by introducing the virus subcutaneously, in the hope that 

 the skin would retain the fluid and the immunizing agent would be gradually 

 absorbed by the tissues. Most of these experiments were conducted in the labora- 

 tory, although one project was carried into the field. These experiments demon- 

 strated very clearly that it is impossible to immunize satisfactorily either chickens 

 or fowls on a large scale by this method, because the skin of the bird is thin, soft 

 and rather porous, so that it does not retain solutions for the absorption of the 

 virus for any great length of time. All of the viruses had to be diluted and filtered, 

 because concentrated un filtered tracheal exudates tended to produce abscesses 

 and suppurations. 



In some of the experiments a physiological saline filtrate of the tracheal exudate 

 containing the virus was mixed with one-half its volume of sterile glycerol before 

 inoculation, in the hope that the mixture would be retained longer and absorbed 

 more gradually by the tissues, as occurs in glycerolized bile (Gibbs, 1925), and 

 antirinderpest serum in cattle (Gibbs, 1929). For some reason not fully under- 

 stood, the results were unsatisfactory under field conditions, although the exper- 

 iments with birds confined in cages were encouraging. The glycerol did not de- 

 stroy the virus, for it had previously been determined that glycerol in one-half 

 its volume of physiological saline solution is one of the best liquid preservatives 

 of infectious laryngotracheitis virus known. 



The following protocol on the subcutaneous inoculation of various preparations 

 of tracheal exudates illustrated the efficacy of the glycerol and physiological saline 

 preparation over the others under laboratory conditions. 



Chickens, two months old, were divided into six groups of 10 each, while a 

 control group of 12 chickens were placed in cages so as to provide two controls for 

 each preparation of virus. The subcutaneous inoculations were made on the 

 sides of the breast, under the wings, as follows: — 



Group 1 was inoculated subcutaneously with 2 cc. of tracheal exudate, diluted 

 1-25 and filtered through sterile Whatman paper to remove the coarse particles. 



