52 EXPERIMENT STATION BULLETIN 351 



made. Work has shown that the time and temperature of the reaction 

 must be very accurately controlled. 



R. C. RiNGROSE, E. F. Waller, T. B. Charles, 

 F. E. Allen, S. R. Shimer, H. A. Davis 



The Etiology, Pathology and Prevention of Contagious Indigestion 



In May 1942, parts of two small flocks were inoculated with the 

 experimental vaccine made with the "Blue Comb" virus. This was re- 

 ported last year but the results were not obtained until September. In 

 the first flock 250 out of 525 pullets were inoculated and raised together 

 on the same range. A second group of birds, six weeks younger, were 

 put on a separate range. In September all birds were housed and the two 

 groups were mixed in the various pens. "Blue Comb" made its appearance 

 in the younger pullets only. In view of some experiences here at the lab- 

 oratory, it is obvious that there was sufficient spread from the inoculated 

 to the uninoculated in the first group to establish immunity in the ma- 

 jority of all of the older birds. 



The second flock contained only 90 pullets of which 45 were 

 inoculated. They were divided into groups and raised on separate 

 ranges with new equipment and new shelters. After these birds came into 

 production a pen of sixteen hens and one male was made up from each 

 group. These two pens were fed fresh tissues from field cases of "Blue 

 Comb." The uninoculated group became depressed, developed a diar- 

 rhea, decreased their feed consumption and their egg production on the 

 third, fourth, and fifth day after feeding and then rapidly returned to 

 normal. The inoculated pen showed no visible eff^ects although they were 

 fed the same amounts of the same tissues and at the same time. This work 

 is being duplicated this spring on a larger scale. Approximately 3,000 

 birds will be inoculated with twice that number as controls on the same 

 farm. 



At first there was difficulty in obtaining sufficient embryonic mem- 

 branes to make the required amount of vaccine. An attempt was made 

 to use the whole embryo. This, dried under vacuum, gave weak and in- 

 consistent reactions. A combination of ground embryos and embryonic 

 membranes were treated with various preservatives such as are used in 

 some other vaccines: namely, formalin, phenol, ether and chloroform. 

 The birds were injected with these preparations and daily blood examina- 

 tions made for six days. Four weeks later they were reinjected with 

 known virulent material. The one containing chloroform was the only 

 one to give any protection and there is some doubt if the bird was im- 

 munized or if had been contaminated from an adjoining pen. Later a 

 new technique for harvesting infected embryonic membranes was de- 

 veloped and the work with the chemically treated product was dropped. 



Four strains of the virus are being carried in eggs at this time. Trans- 

 fers are made at 7 2 -hour intervals. All strains have become more or less 

 constant in their reaction. 



A limited amount of work has been done with turkey and duck eggs. 

 Both are very susceptible if inoculated at twelve days instead of nine and 

 left for 96 instead of 72 hours. The reaction is much more severe and the 

 embryo mortality is greater. Ten duck eggs were inoculated as 12-day 



