EFFECT OF ACIDS ON TYPHOID AND COLON BACILLI 269 



perature in the presence of the acid was very fatal in its effect on the 

 bacteria. 



The typhoid culture used was obtained from the Massachusetts 

 General Hospital, where it had been isolated from the spleen of a 

 clinically typical case of typhoid fever ; the colon bacillus was isolated 

 in the laboratories of the Institute, and both gave all characteristic 

 reactions. Twenty-four-hour agar-slant cultures were used in all 

 cases. 



The tables have been prepared to show, in the first column, the 

 parts per million of the acid, and in the second column the parts per 

 million of acidic hydrogen or, more accurately, of replaceable 

 hydrogen. The third column shows the strength converted into terms 

 of normality. The percentage dissociation of the acids at each dilu- 

 tion is given in the fourth column, and the actual parts of disso- 

 ciated hydrogen in the fifth. The last two columns show the initial 

 number of bacteria used as shown by blank controls and the per- 

 centage reduction after 40 minutes. 



The tables show in general that with increasing quantities of 

 disinfectant the bacterial reduction proceeds rapidly up to a certain 

 point. After 99 per cent of the organisms have been killed, how- 

 ever, it takes a very considerable further increase of acid to produce 

 sterilization. This is a point of very fundamental importance, and 

 one which has been observed in studying the effect of such various 

 agents upon the bacteria, that it deserves special attention. Sedg- 

 wick and one of us (Sedgwick and Winslow, 1902) have called atten- 

 tion to the persistence of a few specially resistant individuals when 

 typhoid bacilli are exposed to the action of cold. After 14 days of 

 exposure to freezing temperature 99.8 per cent of the organisms 

 were killed, but after three months a few still survived. Johnson's 

 tables of the reduction of typhoid and colon bacilli by copper salts 

 (Johnson, 1905) show the same phenomenon, although he does 

 not comment upon it specifically. More recently, Frost and Swenson 

 (1906), and Gage and Stoughton (1906), have emphasized this 

 peculiar phenomenon, in connection with resistance to high tem- 

 peratures. The former authors, working with B. dysenteriae, found 

 that "the majority of the cells were killed between 55 and 60, but 

 that frequently a relatively small number, possibly one individual 



