BY DR. OSCAR KATZ. 207 



by comparing the different modes of growth on the different 

 potatoes with one another, would have thought of there being two 

 absolvitely distinct micro-organisms. But still a mistake could not 

 have occurred, because one and the same gelatine stick-culture had 

 been used in all cases of that kind for the inoculation of the 

 potato-surfaces ; in fact, any mistake was excluded, as something 

 of those grey cultures being transferred to other potatoes resulted 

 in yielding again ordinary, invisible cultures which microscopically 

 showed again normal bacilli and pseudo-filaments. By and by we 

 learnt to distinguish the different sorts of potato, and were thus 

 able, now and then, to anticipate which ones would show invisible 

 and which ones visible colonies. Thus, by mutual transmissions 

 of cultures of one kind of potato to another kind we could 

 occasionally obtain those cultures. All this proves most certainly 

 that with the technic no fault was to be found. We might be 

 permitted to state that in our experiments on animals we worked 

 with the two different looking cultures separately, but the results 

 being always alike in either case we considered later on such a 

 separation as superfluous, and in our subsequent annotations these 

 differences of the culture are no more taken notice of. We 

 want purposely to lay special stress on these striking deviations 

 of the potato-cultures, because, in disregard of this demeanour 

 perhaps many an observer might have arrived at wrong conclusions. 

 By this the value of the potato-culture for the identification of 

 the typhoid-bacillus is by no means lessened, only it is advisable 

 in all such-like cases where a growth corresponding to the one 

 above-described makes its appearance, to transfer the questionable 

 potato-culture to several other potato-surfaces before a decisive 

 opinion should be formed." 



Such mal-formations are probably brought about in consequence 

 of the use of bad, watery potatoes ; the quality of a potato which 

 it is intended to take as nutrient soil for the cultivation of 

 typhoid-bacilli or of any kind of micro-organisms, can easily be 



