256 Cultures, and their Study 



advantage except in cases where it is desired to scatter the 

 transplanted organisms as much as possible, in order that 

 the bacteria will grow, or in order that a large bacterial mass 

 may be secured. 



Cultures upon Potato. These are made by simply 

 stroking the surface of the culture medium, the opacity of 

 the potato making it impracticable to puncture it. 



Cultures in Fluid Media. Here, as has already been 

 stated, transplantation consists in simply stirring in the 

 bacteria so as to distribute them fairly well throughout the 

 medium. 



Adhesion Preparations. Sometimes it is desirable to 

 preserve an entire colony as a permanent microscopic speci- 

 men. To do this a perfectly clean cover-glass, not too large 

 in size, is momentarily warmed, then carefully laid upon the 

 surface of the gelatin or agar-agar containing the colonies. 

 Sufficient pressure is applied to the surface of the glass to 

 exclude bubbles, but not to destroy the integrity of the 

 colony. The cover is gently raised by one edge, and if suc- 

 cessful the whole colony or a number of colonies, as the case 

 may be, will be found adhering to it. It is treated exactly 

 as any other cover-glass preparation dried, fixed, stained, 

 mounted, and kept as a permanent specimen. It is called 

 an adhesion preparation " Klatschprdparat." 



Special Methods of Securing Pure Cultures. Pure 

 cultures from single colonies may also be secured by a very 

 simple manipulation suggested by Banti.* The inoculation 

 is made into the water of condensation at the bottom of an 

 agar-agar tube, without touching the surface. The tube is 

 then inclined so that the water flows over the agar, after 

 which it is stood away in the vertical position. Colonies will 

 grow where bacteria have been floated upon the agar-agar, 

 and may be picked up later in the same manner as from a 

 plate. 



When the bacterium to be isolated (gonococcus, etc.) 

 will not grow upon the media capable of alternate solidifica- 

 tion and liquefaction, the blood-serum, potato, or other 

 medium may be repeatedly stroked with the platinum wire 

 dipped in the material to be investigated. Where the first 

 strokes were made, confluent impure cultures occur; but as 

 the wire became freer of organisms by repeated contact with 

 the medium, the colonies become scattered and can be 

 studied and transplanted. 



* " Centralbl. f. Bakt. u. Parasitenk.," 1895, xvii, No. 16. 



