228 EARL W. FLOSDORF 



tion of the live virus were they not protected simuhaneously witli tlie 

 serum. When used in conjunction with anti-hog cholera serum, the 

 virus possessing high virulence and the proper antigenic properties 

 stimulates a strong, active immunity of lasting duration. The 

 product w^hen dispensed as a liquid must be preserved with phenol in 

 the amount of 0.5%. This agent exerts a virucidal action that gradu- 

 ally reduces the viability until it is no longer infective. For this 

 reason, the United States Bureau of Animal Industry has assigned an 

 expiration dating of only ninety days for the phenolized liquid from 

 the date of the production (not sale) of the product. Accordingly, 

 the results with the freeze-dried product are of particular importance, 

 not only in extending the actual dating, but also in assuring that 

 the product when used will not have undergone partial deterioration. 



Munce and Reichel have also reported that the freeze-dried sam- 

 ples maintained their infectivity for a longer period after freeze- 

 drying when stored in flame-sealed ampules than in rubber-stoppered 

 bottles, in both cases the containers being evacuated. 



Although unpreserved liquid virus maintains its infectivity for a 

 longer period than phenolized liquid virus from the same mixture and 

 stored at the same temperature, governmental regulations require 

 the use of a suitable preservative, for obvious reasons. Accordingly, 

 the results of significance are those comparing the longevity of the 

 freeze-dried product with the phenolized liquid virus. 



2. Bacterial Preservation 



Freeze-drying of stock cultures to avoid continual laboratorj^ sub- 

 culture is a routine practice in most of the more important bacterio 

 logical laboratories today. The method not only results in saving 

 of time and labor, but it avoids the variations that occur with so 

 many organisms after continued laboratory subculturing. 



Hammer applied desiccation for the preservation of numerous 

 viable bacteria (36). Rogers used the method successfully for lactic- 

 acid-forming bacilli (27) . Swift has used this method of desiccation 

 extensively in his work with streptococci and pneumococci (28). 

 Siler and associates at the Army Medical School have maintained 

 their cultures of the now well known S-58 virulent Eherthella hjphom 

 without dissociation over a period of many years {29). Preservaticjn 

 of this strain in this fashion made it possible for Siler and his group 

 to embark on a program of research lasting over a period of years. 



