440 THE BACILLUS OF TYPHOID FEVER. 



upon potato is very important for its differentiation, especially as the 

 common bacilli referred to Bacillus coli communis, bacillus of Em- 

 merich produce a very distinct and rather thick, yellowish- white 

 mass upon the surface of potato. But recent researches show that 

 this invisible growth, although not a common character, does not 

 "belong exclusively to the typhoid bacillus (Babes). 



This bacillus in its development in culture media produces acids 

 according to Brieger small quantities of volatile fat acids, and, in 

 presence of grape sugar, lactic acid. It also grows readily in a de- 

 cidedly acid medium, and this character has been employed as a test 

 for differentiating it from other similar bacilli ; but some of these 

 also grow in a decidedly acid medium, and too much reliance cannot 

 be placed upon this test. 



Brieger has shown that indol is not produced in cultures of the 

 typhoid bacillus, and Kitasato has proposed to use the indol test for 

 differentiating this from other similar bacilli which are said, as a 

 rule, to give the indol reaction. This test consists in the addition to 

 ten cubic centimetres of a bouillon culture which has been in the in- 

 cubating oven for twenty-four hours, of one cubic centimetre of a 

 solution of sodium nitrite (0.02 gramme to one hundred cubic centi- 

 metres of distilled water), together with a few drops of concentrated 

 sulphuric acid. If indol is present a red color is developed. 



None of the above-mentioned tests are entirely reliable, but, taken 

 together with the morphological and biological characters above de- 

 scribed, they may enable the bacteriological expert to give a tolerably 

 confident opinion as to the presence of this bacillus in a water supply 

 suspected of contamination, etc. And when a bacillus having these 

 characters is obtained in a pure culture from the spleen of a typhoid 

 cadaver the student may be very sure that he has the typhoid bacillus. 

 But in the presence of various similar bacilli, as in faeces, very careful 

 comparative researches will be required to determine in a definite 

 manner that a non-liquefying bacillus obtained in pure cultures by 

 the plate method is really the one now under consideration espe- 

 cially so as the cultures of the typhoid bacillus in the same medium 

 may differ considerably at different times, and a number of bacilli 

 are known which resemble it so closely that it is still uncertain 

 whether they are to be considered as varieties of the typhoid bacillus 

 or as distinct species. Thus Babes, in an extended research, found in 

 the organs of typhoid cases, associated with the true typhoid bacillus, 

 other bacilli or varieties very closely resembling it. He has also 

 described three varieties (?), obtained by him from other sources, 

 which could only be differentiated from the true typhoid bacillus by 

 very careful comparison of cultures made side by side in various 

 media. 



