10 



MASS. EXPERIMENT STATION BULLETIN 295 



The results of these inoculations are reported in Table 7. 



Table 7. — The Results of Subcutaneous Inoculation with Hyperimmune 



Serum 



The Duration of Immunity 



A determination of the duration of immunity stimulated by the intravenous 

 inoculation of hyperimmune serum was made by selecting 42 pullets and cockerels 

 and inoculating 30 of them intravenously with hyperimmune serum. The birds 

 were given 1/4 cc. of serum the first day and .3/4 cc. the second. The 12 uninocu- 

 lated birds were held as controls. 



Five days after the serum treatments, 10 inoculated and 4 uninoculated con- 

 trols were picked out of the flock at random, placed in separate cages, and inocu- 

 lated intratracheally with fresh virus. Ten and fifteen days after the serum treat- 

 ments, the second and third groups were treated likewise. The results are noted 

 in Table 8. 



Table 8. — Duration of Immunity Imparted to Pullets and Cockerels by 



Hyperimmune Serum 



This experiment indicates that immunity imparted to pullets and cockerels 

 by hyperinmiune infectious laryngotracheitis serum is temporary. It had evi- 

 dently reached its full strength five days after administration, as indicated by 

 Group 1, but soon after this it apparently began to decline so that at ten days after 

 inoculation 4 of the 10 chickens had contracted the disease, but none died, as 

 shown by Ciroup 2. Fifteen days after inoculation practically all of the immunity 

 imparted by the hyperimmune serum had disappeared, as revealed by Group 3, 

 in which 9 of the 10 chickens contracted the disease and 8 of them died. 



VACCINATION IN THE BURSA OF FABRICIUS 



Since the introduction of antigens directly into the subcutaneous tissues and 

 blood stream did not yield satisfactory methods for immunizing birds against 



