392 PATHOGENIC BACTERIA. 



Indol is formed in both bouillon and pepton solu- 

 tions. Phenol is not produced. Litmus added to the 

 culture-media is ultimately decolorized by the bacilli. 



The presence of indol is probably best determined by 

 Salkowski's method. To the culture i c.cm. of a 0.02 

 per cent, aqueous solution of potassium nitrate and a 

 few drops of concentrated sulphuric acid are added. If 

 a rose color develops, indol is present. 



Nitrates are reduced to nitrites by the growth of the 

 bacillus. 



Upon potato the growth is luxuriant. The bacillus 

 forms a yellowish-brown, glistening layer spreading from 

 the line of inoculation over about one-half to two-thirds 

 of the potato. The color shown by the potato-cultures 

 varies considerably, sometimes being very pale, some- 

 times quite brown. It cannot, therefore, be taken as a 

 characteristic of much importance. Sometimes the po- 

 tato becomes greenish in color. Sometimes the growth 

 on potato is almost invisible. 



In milk there are rapid coagulation and acidulation, 

 with the evolution of much gas. 



The bacillus seems to require very little nutriment. It 

 grows in Uschinsky's asparagin solution, and is frequently 

 found living in river and well waters. 



It is quite resistant to antiseptics and germicides, and 

 grows in culture-media containing from o. i-o.z per cent. 

 of carbolic acid. It lives for months upon artificial 

 media. 



The bacillus begins to penetrate the intestinal tissues 

 almost immediately after death, and is the most frequent 

 contaminating micro-organism met with in cultures made 

 at autopsy. Exactly how it penetrates the tissues is not 

 known. It may spread by direct continuity of tissue, or 

 ria the blood-vessels. 



While under normal conditions a saprophytic bacte- 

 rium, the colon bacillus is far from harmless. It not 

 infrequently is found in the pus of abscesses remote from 

 the intestine, and is almost always found in suppura- 



