TYPHOID BACILLUS 



327 



matter, as feces. Cultures exposed to temperatures from C. to 

 10 C. for three months occasionally contain viable organisms. 

 Alternate freezing and thawing is more fatal than simple freezing. 

 The typhoid bacillus dies out rather rapidly in potable water, less 

 rapidly in sterilized potable water. The addition of organic matter, 

 particularly of fecal origin, appears to promote longevity somewhat. 

 The observations of Jordan, Russell and Zeit 1 would indicate that a 

 large percentage of organisms exposed in potable water die within 

 three days. Kersten 2 has shown that typhoid bacilli will develop 

 with considerable rapidity in raw milk. The bacilli may remain alive 

 in soil for several months, provided they are shielded from direct 

 sunlight, and they may resist drying under similar conditions for 



FIG. 47. Bacillus typhosus, bouillon culture. X 1000. 



several weeks. A maximum exposure of from four to eight hours to 

 direct sunlight in the months of June, July and August (Northern 

 Hemisphere) usually kills the organisms. Mercuric chloride 1 to 1000 

 kills the naked germs in about ten minutes; 5 per cent, carbolic acid 

 kills them in from five to ten minutes, as a rule. 



Products of Growth. The typhoid bacillus liberates ammonia from 

 protein in sugar-free media, and forms small amounts of non-volatile 

 alkaline products as well. The reaction, therefore, becomes progres- 

 sively alkaline. A radical change in the nature of the products of 

 metabolism occurs when the bacilli are grown in protein media con- 

 taining utilizable carbohydrates, as dextrose or mannite. The reaction 

 becomes strongly acid, due to the fermentation of the sugar. The 



1 Jour. Infec. Dis., 1904, i, 641. 



2 Arb. a. d. kais. Gesamt., 1909, xxx, 341. 



