ANAEROBIC BACTERIA 169 



agar cylinder is then cut up into fine slices by means of a sterile scalpel; 

 the desired colony is selected, either with the naked eye or using the 

 microscope, and the agar is carefully cut away from it. A transfer is 

 then made by pricking the colony with a fine sterile platinum needle 

 and inoculating deep tubes with sterile agar or slants and liquid media, 

 which are then incubated in an oxygen-free atmosphere. 



When single cells are separated from one another to obtain pure cul- 

 tures, it is better to isolate the spores rather than vegetative cells, since 

 these give a much larger number of successful cultures (Barber). A 

 medium somewhat more acid than the optimum (as pH 6.0) is more 

 favorable for the germination of the spores. Semi fluid media (con- 

 taining 0.1 to 0.2 per cent agar) are preferable to liquid media, since the 

 presence of a colloid greatly hastens the germination of the bacterial 

 spores. 33 



Further information on the isolation of anaerobic bacteria is given 

 elsewhere. 34-39 



Cultivation of anaerobes. There are a number of methods available 

 for the cultivation of anaerobes, these methods being largely concerned 

 with the reduction of the oxygen tension; some of these have been re- 

 ferred to already previously. 



I. Cultivation in the absence of oxygen: 



1. Mechanical protection against the atmospheric oxygen. The use of large 

 volumes of freshly-boiled liquid media placed at a high level; also the process of 

 covering the media with a laj-er of liquid petrolatum or other inert oil has been 

 known since Pasteur. A layer of solid medium can be placed in a Petri dish, then 

 inoculated with anaerobic bacteria and covered with a solution of agar (1.2 to 

 1.5 per cent) in distilled water. This layer of agar, in covering the medium, 

 prevents sufficiently the admission of oxygen. The solid medium may also be 



33 Lantzsch, 1921 (p. 620). 



34 Kursteiner, 1907 (p. 162). 



36 Veillon, A., and Maz6, P. De l'emploi des nitrates pour la culture et l'isole- 

 ment des microbes anaerobies. Compt. Rend. Soc. Biol., 68: 112. 1910. 



36 Northrup, Z. A simple apparatus for isolating anaerobes. Jour. Bact. 1: 

 90-91. 1916. 



37 Hort, E. C. The cultivation of anaerobic bacteria from single cells. Jour. 

 Hyg. 18: 361. 1920. 



38 Fuhrmann, F., and Pribram, E. Die wichtigsten Methoden beim Arbeiten 

 mit Bakterien. Abderhalden's Handb. biol. Arb. Methoden. XII: 483-702. 

 1924. 



39 Lowi, E. Zur Technik der Anaerobenkultur mittels des Pyrogallolverfah- 

 rens. Centrbl. Bakt. I, Orig., 82: 493-496. 1919. 



