BY DR. OSCAR KATZ. 205 



layei* of quite transparent solidified gelatine (or agar-agar). For 

 stick-cultures I used a 6 p.c. nutrient gelatine ; for streak-cultures 

 (on an inclined surface) the same, and occasionally a 1 p.c. nutrient 

 agar-agar. 



Now it need scarcely be mentioned that, from the mere 

 behaviour of pure cultures in stick and in streak of the typhoid- 

 bacillus, from the appearance of its colonies in diverse nutritive 

 substances either on macroscopical observation or on being viewed 

 with low-magnifying powers, and then from the image of the 

 individual bacilli out of such cultures or out of organs under high 

 powers of the microscope, an exact inference as to their undoubt- 

 edly belonging to the Bacillus typhi abdominalis cannot be drawn. 

 With regard to the last-named point I can confirm the statements 

 of others, namely, that the dimensions of the rods are not 

 constant, and that these variations depend in the main on the kind 

 of the nourishing material, out of which cultures of the microbe 

 are microscopically examined. 



Even the staining reaction of the typhoid-bacilli which become 

 discoloured after the method of Gram (see Fliigge, Microorganis- 

 men, p. 643, or any book dealing with the methods of investigation 

 in Bacteriology) cannot be any more maintained as being diagnostic 

 of these schizomycetes, as a bacillus isolated by Escherich from the 

 feeces of young children, and called by him Bacterium coli commune 

 (Fliigge, Microorganismen, p. 269) exhibits the same peculiarity if 

 treated after Gram's method. The only decisive means, so far as 

 known, enabling us to distinguish typhoid-bacilli from all other 

 bacteria, is rather their chai-acteristic growth on slices of boiled 

 potatoes ; in the repeatedly named work of Fliigge full particulars 

 may be had. By subsequent study of the bacilli, however, it has 

 been noticed by several investigators that these do not always grow 

 on the potato-surface in the shape of a coherent, resisting membrane 

 which was considered as typical by GafFky, the first who worked 

 with pure cultures of the bacilli, but that now and then they also 



