36 MICRO-ORGANISMS IN AVATPJR 



tified. A low power, magnifying about 100 times, is all 

 that can be used for this purpose. The plate is removed 

 from the moist chamber and placed on the stage of the 

 microscope, which must be so constructed as to permit 

 of the plate being shifted about that all the colonies 

 can be brought into the microscopic field. Each colony, 

 if it has had space to develop freely, is almost invariably 

 a pure culture, so that by removing a portion of any 

 particular one by means of a sterile platinum-needle to 

 a test-tube containing gelatine or other culture material 

 the growth may be perpetuated in a state of purity. 

 This ' fishing out ' of the colonies is easy when there 

 are only a few on the plate, but when numerous 

 and crowded together it is difficult to ensure pro- 

 curing the particular one which is in request and which 

 can possibly only be distinctly seen under the micro- 

 scope. 



To facilitate this, ingenious contrivances have been 

 introduced by Fodor 1 and Unna. 2 



Of these instruments it is sufficient to say that Fodor's 

 consists of a vertical, adjustable stand (somewhat similar 

 to that of a microscope), carrying a piece into which 

 the glass rod of the platinum-needle can be horizontally 

 clamped; this piece is adjustable in a horizontal plane, 

 and the extremity of the needle is bent vertically down- 

 wards for a length of about -J- inch. The plate-culture 

 being placed under the low power of the microscope, 

 and the colony to be removed being visible in the field, 

 the above instrument is approached until the extremity 

 of the needle can be seen with the naked eye to be in 

 the vicinity of the colony in question, but clear of the 

 gelatine-film. The operator then makes the final adjust- 

 ments with the instrument whilst viewing the colony 

 through the microscope ; by depressing the vertical 



1 Fodor, Centralbl. f. Bakteriologie, x. 721. 3 Unna, ibid. xi. 278. 



