APPENDIX TO CHAPTER XL 



A VERY useful method for the isolation of a mixture of 

 bacteria is the one now extensively used by Koch and his 

 school, it is this : liquefy over gentle heat sterile gelatine 

 mixture (gelatine and peptone, or gelatine, peptone, and broth, 

 as mentioned on p. 15) contained in a sterile plugged test- 

 tube, then inoculate this with the smallest trace of the bacterial 

 mixture, either by capillary pipette or by a platinum wire, shake 

 it so as to distribute the introduced bacteria ; then pour this 

 liquid gelatine mixture in a thin layer on sterile glass plates, 

 or flat watch-glasses or any glass vessel, and keep this in a 

 closed chamber (a bell-glass or any other vessel fixed by olive 

 oil or lard to a glass plate) kept moist by wet filter-paper. 

 Keep this in the temperature of the room, or in the incubator, 

 up to a temperature of 20 C., so that the gelatine layer remains 

 solid. After several days a number of isolated spots will be 

 noticed, each of these spots owing their origin to the multipli- 

 cation of a bacterium. Some of these spots contain only one 

 species, and from these pure cultivations in test-tubes can then 

 easily be established. In this way Koch easily succeeded to 

 isolate the comma-bacilli present in the mucus-flakes of the 

 choleraic intestine, a small particle of such a flake being 

 distributed in the liquefied gelatine mixture contained in a 

 test-tube. 



Another method of isolation is one similar to that described 

 on p. 31 : Liquefied sterile gelatine mixture, or liquefied 

 sterile Agar-Agar mixture, is poured in a thin layer on the 

 glass plates, watch-glasses, or glass-cells previously sterilised, 

 and then kept in a moist chamber as above. When the mix- 

 ture is set, draw on its surface lines with a capillary tube or 

 platinum wire dipped in the bacterial fluid. 



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