CUTANEOUS VACCINE FOR FOWL POX 253 



number of colonies on four plates was 1.0 at the end of 567 hours, and the 

 average number of colonies on four slants was at the same time. The ex- 

 periment was concluded at this point. 



It seems reasonable to believe that, if the glycerol content of the stand- 

 ard vaccine had such an effect on the contaniinators, it w-ould also have a 

 relatively similar eifect on the filtrable virus. The results of the experiment 

 indicate that this is so. 



A 40 per cent content of glycerol has always been used in the standard 

 cutaneous vaccine. Its disinfecting action, as shown above, precludes the use 

 of phenol in the vaccine as a preservative. This content of glycerol serves to 

 aid greatly in keeping the virus in s.uspension. There seems to be no reason 

 for increasing the content of glycerol. It is probable that if the percentage 

 were decreased the attenuation would not be so great. But after all, a low 

 expiration date on a vaccine of this type is desirable, for it emphasizes the 

 fact that the vaccine should be used when comparatively fresh. It has been 

 repeatedly demonstrated that the nnattenuated vaccine is the only efficient 

 preventive against fowl pox. 



Summary 



Following a brief historical sketch of the subject, the cutaneous vaccine 

 for fowl pox isi described. Recommendations for its use and practical ad- 

 ministration are given. 



Two flocks containing 2,4-16 birds A\ere vaccinated cutaneously just before 

 being placed in the winter laying quarters. They remained free of fowl pox 

 throughout the year. Annual outbreaks of the disease had occurred in these 

 flocks for the four previous years. The gradual increase in early egg pro- 

 duction was slightly retarded subsequent to the vaccination, beginning on the 

 eighth or ninth day and ending on the twenty-first day after the treatment. 

 The results of the work indicated that it was safe to vaccinate birds cutane- 

 ously as they were transferred from the range to laying houses, even though 

 they were in early egg production at the time. 



A slight increase in rectal temperature, averaging less than 1° F., occurred 

 following cutaneous vaccination. The vaccination did not result in a retarda- 

 tion in the gain in weight of 80-day-old and 210-day-oId birds. A slight 

 retardation in gain in weight did occur, however, in 68-day-old birds. These 

 results, however, were not considered as evidence against the vaccination of 

 birds of such an age in such a manner. 



The 100 milligram vaccine produced follicular swellings and scab 

 formations comparable to the standard, the 300 milligram, and the commer- 

 cial vaccines on birds of 68 and 80 days of age. Therefore, its use appeared 

 to be indicated on birds of these ages. 



The use of the standard cutaneous vaccine in a flock that was in the 

 early stages of fowl pox infection and but slightly afipected, apparently pre- 

 vented further spread of the infection. 



The results of inoculations with virulent virus suspensions on the combs 

 of cutaneously immimized birds indicated that the duration of immunity was 

 at least 371 days. 



The glycerol content of the diluent had a decided inhibitory and disin- 

 fectant action on the contaminating organisms in the vaccine. Assuming that 

 it had a relatively similar eflfect on the filtrable virus of the vaccine, the at- 

 tenuation of the cutaneous vaccine as a result of aging may be thus explained. 



