Hitchner in 1950 (5) ohserved that ])ai"fntal iniunniit\ nuiy he over- 

 come in day-old chicks, and that imninnit\' from da\-iild vaccination mav he 

 ohtained even in the face of parental immnnitw 



Hitchner and Keising in 1952 (6j, however, demonstrated hy labo- 

 ratory and field trials that atomization of the H, strain of virns offered a 

 l)ractical method for vaccinating and revaccinating hirds ^ weeks old or 

 older. By such administration, successful revaccination was accomplished in 

 l)roiler flocks 4 weeks old after intranasal vaccination at one day of age. Re- 

 placement flocks revaccinated at 15 to 20 weeks of age demonstrated a good 

 antigenic res])onse. 



It was noted also hy Hitchner and Keising in this same study that the 

 Bj strain of virus produced a greater reaction when administered to chicks 

 as a spray than when administered intranasally. The respiratory reaction 

 varied from flock to flock with negligi])]e mortality exce])t in those cases 

 where it appeared that a concurrent infection was |)resent. 



Luginhuhl {^>) was one of the first workers to combine the vaccinations 

 of Newcastle and infectious l)ronchitis at an early age. The administration 

 of this vaccine involved the intranasal route applied to each bird. 



Crawley in 1953 (2) and 1954 (3) has demonstrated that chicks could 

 ])c inoctflated by a spray technique from one da_\" of age up to 20 weeks. It 

 was observed that the com])ination of infectious bronchitis virus and New- 

 castle disease virus into one vaccine produced less interference in growth 

 when the 2 vaccines were applied at the same time than if given separately 

 In regards to Crawley's work it has been found by many investigators dif- 

 ficult to duplicate Canadian results under American field conditions. 



Candling embryos in preparation for vaeoine prodiu'lion. 



4 



