IMMUNOLOGY OF LARYNGOTRACHEITIS 11 



infectious laryngotracheitis, it was decided to try the bursa of Fabricius, since 

 this organ is lined with mucous membrane, and is some distance from the respira- 

 tory tract. Up to this time it was not known that the bursa of Fabricius was 

 susceptible to inoculation with infectious laryngotracheitis. After this point had 

 been determined, Hudson and Beaudette (1932) published their results on the 

 cloacal inoculation of chickens with infectious laryngotracheitis virus; and 

 after the work reported in this bulletin had been completed, they published their 

 "F.xperiments on Immunization against Laryngotracheitis in Fowls" (1933). 

 The work is based on the same principle as the experiments reported herein, 

 although the method of attack, field covered, and interpretation of results differ 

 in several important respects. However, Beaudette and Hudson have had some 

 access to field work, and probably speak with authority on the practical value of 

 this method for immunizing birds outside of the laboratory. 



The Bursa of Fabricius 



The bursa of Fabricius, named after Hieronymus Fabricius, the celebrated 

 Italian anatomist and surgeon (Borden, 1922), is a bulblike organ lying dorsally 

 to the cloaca in the chicken. It is fully tleveloped at the time of hatching, con- 

 tinues to increase in size as the bird grows, and reaches its maximum development 

 between four and five months (Schauder, 1923; Otte, 1928). At this time it aver- 

 ages one inch long, three-fourths of an inch wide, and one-tenth of an inch in 

 thickness in the Rhode Island Red. It occurs in both cockerels and pullets. 

 Involution commences near the time of sexual maturity (Jolly, 1913; Riddle, 1928), 

 and in the course of two or three months it is reduced to a narrow fold. 



The wall of the bursa of Fabricius is made up externally of a serosa composed 

 chiefly of white fibrous connective tissue, and an internal mucous membrane lined 

 with epithelial tissue. A layer of circular and longitudinal involuntary muscle 

 tissue is located between the serous and mucous membrances. The mucous mem- 

 brane and some of the muscle tissues are folded longitudinally so that the organ 

 presents a wrinkled appearance internally. The external appearance is smooth. 

 The aperture into the bursa of Fabricius is small and controlled by a sphincter 

 muscle until involution commences. At the time of retrogression, the sphincter 

 muscle gradually loses its elasticity and the opening enlarges until involution is 

 complete. In the adult bird the opening appears as a horizontal slit leading into 

 the bursal fold. 



The physiological function of the bursa of Fabricius has been disputed. Retter- 

 er and Lelievre (1913) believed it to be concerned in fertilization. Jolly (1911) 

 ascribed a hematopoietic function to it, and Jolly and Levin (1911) stated that it 

 might be associated with nutrition for it degenerates rapidly during starvation, and 

 is abundantly supplied with lymphatics. 



Infection of the Bursa of Fabricius with the Virus of Infectious 

 Laryngotracheitis 



In starting these experimental studies on the bursa of Fabricius inoculation, it 

 was necessary first of all to determine whether this organ could be infected with the 

 virus of infectious laryngotracheitis, and if so, how long the virus would remain 

 in it. 



Twenty-four chickens three months old were selected for this study. Twelve 

 of them had never been exposed to the disease, and the others had been immunized 

 by the intravenous method. All of them were inoculated in the bursa of Fabricius 

 with infectious laryngotracheitis virus, which had been prepared in the following 



