190 METHOD OF CULTIVATING MICRO-ORGANISMS ON POTATOES. 



also in this case any appreliensions of the danger of desiccation 

 must disappear. However, it is advisable, whenever we have a 

 larger supply of such prepared potatoes, to put an indiai'ubber- 

 •cap on the opening of the tubes over the cotton-wool stopper, 

 or to tie some indiarubber-tissue round it. 



One thing still needs mention, namely, that we are able 

 to avail ourselves of both the surfaces of the potato-slices since 

 these are mounted so as to occupy a middle position in the lumen 

 of the test-tubes (p. 189, fig. 2). We can inoculate both these 

 surfaces either with one and the same microbe, taken from one 

 and the same colony or cultui'e, or we can also easily cultivate on 

 the one side one organism, on the other a difierent one. 



The latter mode may sometimes prove to be a matter of some 

 convenience; for instance: in cultivations on plates of gelatine 

 after Koch, or in test-tubes with gelatine after Esmarch, made 

 from stools of typhoid fever patients, there appear after some time 

 different kinds of non-liquefying colonies which grow nearly at the 

 same rate, exhibit under high powers of the microscope similar 

 forms, and which it must be desirable to cultivate on boiled 

 potatoes in order to find out which ones appertain to the bacillus 

 of typhoid fever. In this case, then, we might transfer to the one 

 side of the potato-discs a minute quantity of one colony, to the 

 other side, while still holding the glass tube in our left hand, a 

 little of another, somewhat different-looking colony. 



In conclusion I may add that test-tubes of the above description 

 seem also well adapted for the cultivation on and in gelatine after 

 Esmarch's method (Zeitsch. f. Hygiene, herausgeg. von Koch und 

 J'lugge, Band I., Heft 2, Leipzig, 1886, pp. 293-301). 



