CUTANEOUS VACCINE FOR FOWL POX 251 



vaccines. Apparently the only differences between the lesions produced by 

 the two groups of vaccines were their extensiveness and severity. Beach was 

 inclined to believe that this change "in the virus content as a result of aging 

 was more probably a decrease in amount due to the death of part of the virus 

 than to a decrease in virulence". 



The results obtained by the writer {'S) were similar to some degree to 

 those just described. The standard vaccine, administered at intervals of 6, 11, 

 16, 19, and 25 days after manufacture, produced pox eruptions (follicular 

 swellings and scab formation) all in comparatively the same period of time. 

 The follicular reaction resulting from the vaccine administered on the twenty- 

 fifth day was just as severe and prominent as that administered on the sixth 

 day. When the vaccine was administered on the thirty-first, fortieth, and 

 forty-sixth day after nvanufacture a follicular swelling developed, but not the 

 u,s|ual scab formation. It was evident that the standard vaccine became at- 

 tenuated after 25 days of aging. 



The following experiment was designed to determine whether the glycerol 

 might be the cause of this attenuation. Glycerol was used in Beach's vaccine 

 and probably was the cause of the evident "death of part of the virus". It 

 was also borne in mind that the results of such an experiment might indicate 

 some method by which the tentative method of standardizing the cutaneous 

 vaccine (3) could be improved upon. 



The action of the glycerol on the virus content of the vaccine necessarily 

 had to be approached in an indirect manner. It has been shown that pow- 

 dered fowl pox scabs contain, in addition to a filtrable virus which is the active 

 cause of the disease, several contaminating organisms (8), such as Pseudo- 

 monas aeruginosa and various staphylococci. If the glycerol in the diluent 

 inhibited the midtiplication of these contaminators or disinfected them, it is 

 reasonable to believe that the glycerol would affect the filtrable virus in a 

 similar manner. 



TecJinic . 



Virus of known virulence was used in making the standard and control 

 vaccines; that is, it produced pronounced lesions of fowl pox within four to 

 seven days after inoculation on scarified comlbs of susceptible birds. The 

 standard vaccine contained 200 mgm. of virus suspended in 50 cc. of sterile 

 40 per cent glycerol-physiological saline solution. The control vaccine con- 

 tained the same amount of virus suspended in sterile physiological saline solu- 

 tion alone. Immediately after manufacture and at times as stated in Table 

 4, both vaccines were cultured on agar slants and in poured Petri culture 

 dishes of standard size. At first, slecond, and third dilution, plates were 

 poured, but as these were sterile after incubation they were discontinued. 

 When not in use the two vaccines were kept in an electric refrigerator at a 

 temperature of from 45° to 50° F. 



The agar used was made according to the usual formula of Bacto Pep- 

 tone 10 grams, NaCl 5 grams, Liebig's beef extract 5 grams, Bacto Agar 20 

 grams per liter of distilled water. The hydrogen ion concentration was cor- 

 rected to pH 7.2. Twelve centimeters of agar were used in the tubes for 

 pouring plates. 



At all times when the two vaccines were cultured, four plates were 

 poured and four slants inoculated for each vaccine. One-tenth of 1 cc. of 



