350 THE BACILLUS OF TYPHOID FEVER. 



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. 



Cassedebat, also, in an extended examination of the river water 

 at Marseilles with reference to the presence of the typhoid bacillus, 

 found three species which very closely resembled it, but which by 

 careful comparison were shown to present slight but constant dif- 

 ferences in their biological characters. He was not able to find the 

 true typhoid bacillus, and his researches, together with those of Babes 

 and other recent investigators, make it appear probable that numerous 

 mistakes have been made by bacteriologists who have reported the 

 finding of the typhoid bacillus in river and well water, in faeces, etc., 

 and who have depended mainly upon the character of invisible 

 growth upon potato in making their diagnosis. Cassedebat states 

 that all three of his pseudo-typhoid bacilli corresponded in their 

 growth upon potato with the bacillus of Eberth. They also corre- 

 sponded in their growth on gelatin, agar-agar, and blood serum, 

 which, as heretofore remarked, has no characteristic features. They 

 all gave a negative indol reaction. Like the typhoid bacillus, they 

 grew in milk without causing coagulation of the casein, but two of 

 them produced an alkaline reaction in this fluid, while the third cor- 

 responded with the typhoid bacillus in producing a decided acid re- 

 action. Differences were also observed in bouillon cultures, and in 

 bouillon and milk to which various aniline colors had been added, as 

 recommended by Holz. 



Whether the typhoid bacillus, as obtained from the spleen of a 

 typhoid cadaver, is in truth specifically distinct from these similar 

 bacilli, or whether they are all varieties of the same species, result- 

 ing from modifications in their biological characters acquired during 

 their continuous development under different conditions, is an un- 

 settled question. But, in view of the experimental evidence now 



