168 CLINICAL BACTERIOLOGY. 



only with typhoid-bacilli. It is, however, not constant. There 

 are varieties of potato upon which the bacilli of typhoid fever 

 develop in yellowish or brownish, raised, and sharply circum- 

 scribed deposits, and generally upon potatoes whose surface 

 yields a neutral or even an alkaline reaction. Such visible 

 growth can be obtained also artificially by rendering the surface 

 to be inoculated of alkaline reaction. Typical characteristic 

 growth takes place only when the potatoes exhibit an acid reac- 

 tion, which they do, as a rule. 



In milk the typhoid-bacillus induces slight formation of acid, 

 but never coagulation. In Petruschky's whey (p. 86) the 

 typhoid-bacillus generates not more than three per cent, of acid, 

 whereas the bacterium coli commune generates more than seven 

 per cent. 



Bouillon is rendered turbid by cultures of the typhoid-bacillus. 



The typhoid-bacillus does not induce fermentation in nutrient 

 media containing grape-sugar, milk-sugar, or cane-sugar ; nor 

 does it form indol in a solution of peptone and sodium chlorid. 



If potassium nitrite and sulphuric acid are added to peptone- 

 cultures, a red coloration does not occur (p. 122, bacterium 

 coli commune). 



The typhoid-bacillus, as well as the bacterium coli commune 

 and the entire group of bacteria resembling both, is character- 

 ized by a certain degree of resistance to carbolic acid, addition 

 of which to the nutrient medium in the proportion of ^ per 

 cent, not inhibiting the bacilli in their growth. 



Vital Activity of the Typhoid-bacillus. Typhoid- 

 bacilli retain their vitality in sterilized water for a considerable 

 time (up to three months) ; they may even, at least at first, 

 multiply therein. In unsterilized water they die in the 

 course of two weeks, in consequence of the activity of the 

 water-bacteria, by which they are suppressed, and more 

 quickly in running water than in stagnant water. Under 

 favorable conditions, protected from light, evaporation, and 

 competition, they may persist for a long time. Milk may 

 at times contain living typhoid-bacilli for as long a period 

 as five weeks. In the slime of streams and of wells typhoid- 

 bacilli retain their capability of development for not less 

 than three weeks. Buried in the superficial layers of the 

 earth, they have been demonstrated in a living state after 

 five and a half months. They appear also capable of per- 

 sisting for an equal length of time in the feces for three 

 months and more ; naturally only when too many putrefac- 

 tive bacteria are not present at the same time. Typhoid- 



