540 J. 0RSKOV 



all of which, including Burri's method, he rejects, he suggests 

 a new method of isolation ha\ing two modifications, one in 

 which examination is undertaken with an oil-immersion lens, 

 and one in which a dry lens is employed. 



In bacteriologic Uterature, Hort is thus the first to point 

 out that it is possible to see bacteria distinctly on the surface of an 

 agar plate and to watch their growth by means of a high-power 

 system of dry lenses without any staining or contrast. It is true 

 that HiU, in his work on the morphology of the diphtheria bacil- 

 lus, mentions that diphtheria baciUi can be seen distinctly on 

 agar by means of a high-power dry lens, but he does not seem to 

 reaUze the possibUities involved in tliis fact. It is no doubt 

 possible, and I think, probable, that others too have been aware 

 of this fact; Hort is however, as stated, the first who has defined 

 it and understood how to make use of it. 



The medium which Hort employs in his examination, he pre- 

 pares in a manner similar to the one originally appUed by me. 

 He pours the hot agar over sterile slides in as level a layer as 

 possible, taking care to keep the agar well within the edges of 

 the shde. The mode of procedure now varies as to whether he 

 employs the oil-immersion lens, or the chy lens system for further 

 examination. In the first case a series of sterile covershps have 

 been previously prepared, each with a small circle etched on its 

 surface by means of a diamond. In the center of this circle, 

 a minute droplet of broth is now deposited, taken from a broth 

 culture containing the bacteria under investigation in a suitable 

 emulsion. The inoculated coverslip is now placed face down- 

 wards on the agar surface; the area within the small circle is 

 thoroughly examined with an oil-immersion lens, and, in case 

 only one single organism is found witliin the circle, the slide is 

 placed in a Petri dish which is then placed in the incubator. 

 The circle is examined at short intervals, until a small colony 

 has formed from which subcultures can be prepared. 



Hort himself remarks, in regard to tliis procedure, that great 

 care must be taken to ensure that the droplet does not run out- 

 side the etched circle when the coversUp is appUed to the agar, 

 adding, however, that with some care this is easily avoided. It 



