PHYSICO-CHEMICAL PROPERTIES 65 



sealed ampules and test tubes with cotton stoppers. It appeared to 

 this author that if the filtrates ^vere adjusted to pH 5.6 and 6.0, 

 the actix ity persisted longer than when adjusted to pH 8.0. 



The skin-preparatory potency of "agar washings" ciUtine hl- 

 trates of Vibrio cholerae prepared by Uyeda \vas preserved in the 

 pH ranging from 4.6 to 8.5. 



Apitz noted that adjustment to pH 10.0 strikingly increased 

 the activity of P fractions obtained in the coinse of his fractiona- 

 tion of bacterial filtrates described later in this chapter. 



EFFECT OF UFTRAVIOLET RADIATION UPON ACTIVE PRINCIPLES 



Welch (1930) carried out comparative experiments on the 

 effect of racUation with ultraviolet light upon various substances. 

 It was absolutely necessary to use materials prepared in stich a 

 manner that no protein or extremely small amounts of it were 

 present. The medium of Cahn-Bonner Avas used. 



This atithor reported that detoxification of active filtrates of 

 B. coli and B. iypliosus culttires may result from ultraviolet radia- 

 tion. The skin-preparatory factors disappeared Avithin shorter pe- 

 riods of exposure than the reacting factors. It ^vas mentioned in 

 Chapter i that B. typhosus culttne filtrates may have a skin- 

 preparatory potency approximating one-fourth of the reacting 

 titer. It is apparent, therefore, that the partial destruction of the 

 active principles may result in a proportionately lower skin-pre- 

 paratory than reacting titer. Similar observations were made by 

 me on partial detoxification of active principles by means of 

 formalin. 



EFFECT OF DISSOLUTION AND AUTOLYSIS UPON THE ACTIVE 



PRINCIPLES 



As it became obvious from the experiments described in the 

 preceding chapter, bacterial autolysis is not necessary for prepara- 

 tion of the active principles. The asstmiption is first clearly 

 demonstrated by the fact that fluid culttnes of B. typhosus in- 

 cubated for several days usually yield active principles one hun- 

 dred times weaker than filtrates of ^vashings of growth on solid 

 media incubated only for twenty-four hours. Cultures of menin- 

 gococcus in enriched media, inctdjated for periods as long as 

 seven days, and stdijected to alternating freezings and thawings 

 have irregular and low' potency. On the other hand, as mentioned 



