178 CLINICAL BACTERIOLOGY. 



power may appear earlier or later, and in greater or in less 

 degree, and it may even be entirely absent, as these observ- 

 ers have noted, although but once among 163 cases. 



The examination of water for typhoid-bacilli is of 

 great practical importance, as in most epidemics the drink- 

 ing-water is to be considered as the vehicle for the typhoid 

 virus. For this purpose carbolic acid is employed, being 

 added to the suspected water in such amount that this shall 

 contain from 0.05 to 0.25 per cent, of the acid. This addi- 

 tion is made for the purpose of inhibiting the activity of 

 the bacteria present in water that liquefy gelatin ; the 

 typhoid-bacilli themselves readily withstand such slight 

 additions of carbolic acid. With the carbolized water three 

 plates are made in the customary manner, according to the 

 method of Eisner. As by this means only small amounts 

 of water are subjected to examination, it is easily possible 

 that typhoid-bacilli may escape detection, even when pres- 

 ent. It is, therefore, well to subject considerable amounts 

 of the suspected water to examination. To this end a 

 sterilized, alkaline, concentrated solution of peptone and 

 sodium chlorid is employed that contains in a specified 

 number of cubic centimeters one gram of peptone and one 

 gram of sodium chlorid. This amount is added to 100 

 cu. cm. of the carbolized water in an Erlenmeyer flask, 

 and the mixture is placed in the thermostat for from eigh- 

 teen to twenty-four hours. If typhoid-bacilli are present 

 in the water, in some degree protected against the compe- 

 tition of the other bacteria by the addition of carbolic acid, 

 they undergo multiplication, and they can be more readily 

 demonstrated on plates prepared from the mixed cultures. 

 The identification with certainty of the developing suspi- 

 cious colonies as typhoid-colonies is, however, again at- 

 tended with considerable difficulty. The water contaminated 

 by typhoid dejections naturally always contains also the 

 bacterium coli commune, and besides there are frequently 

 present in the water other nonpathogenic bacilli that bear 

 an extraordinary resemblance morphologically and in cul- 

 ture to the typhoid-bacillus so-called pseudotyphoid- 

 bacilli. These, however, sometimes yield the indol-reaction 

 and sometimes not. A considerable number of these bac- 

 teria also develop in the mixed cultures, and a number 

 even much better than the specific typhoid-bacilli. A de- 

 cision as to the presence of typhoid-bacilli in water may 



