538 J. 0RSKOV 



bacteria, which he views in a small hanging-drop of broth, and 

 to inoculate four broth test tubes with each of them separately, 

 one feels predisposed to doubt the possibility of ever acquiring 

 such practice. 



The method most generally used at present is, no doubt, 

 Burri's India ink method, which is the starting point for the pro- 

 cedure described in the followdng communication. As is well 

 known, the principles of the India ink method are, briefly stated, 

 these: the bacteria are emulsified in diluted India ink, of which 

 emulsion minute droplets are deposited on a gelatin plate in a 

 Petri dish by means of a mapping-pen. Those droplets which, 

 by microscopical investigation with a high power dry lens, prove 

 to contain only one single cell, are noted and allowed to stand 

 until a small colony has developed, from which subcultures are 

 prepared ; or, the India ink droplet is removed, together with the 

 bacterium, by means of a sterUe coversUp that is superimposed 

 on the black spot of the gelatin plate, removed again together 

 with the India ink and the bacterium, and dropped into an 

 appropriate fluid nutrient medium. This is, as has been said, 

 an excellent method, by means of which, with some practice 

 and patience, rehable single-cell cultiires of most species of bac- 

 teria can fairly easily be produced. (It is, however, not all 

 bacterial species that will stand the India ink.) 



A drawback in Burri's method is the necessity of having the 

 unhandy Petri dish standing on the microscope stage during 

 the examination. Therefore, I devised a modification: by means 

 of sterile Pasteur pipettes I poured liquid gelatin upon previously 

 sterilized slides. On the gelatin surface three rows of India ink 

 droplets were deposited, which could now be much more easily 

 and rapidly examined by shifting the mechanical stage, the se- 

 lected India ink droplets being subsequently removed as usual 

 by means of sterile coverslips. 



If it is desired to trace the development of the new formed 

 elements on the gelatin, the slides are placed in a sterile Petri 

 dish with a piece of moist filter paper at the bottom. In this 

 way the India ink spot can be examined at intervals, and the 

 development can be observed. The image however, will rapidly 



