J 223 



out as a whole. One maj also with a file make an incision in the 

 glass wall in the neighbonihood of favourably situated colonies. But 

 it is clear that there is much chance that thereby also different colonies 

 intermix so that of a pure culture of anaerobes in the usual sense 

 of the word there is no question in such experiments. For exami- 

 nation with the microscope and for studying the appearance of the 

 colonies the method is useful, but for the culture of pure species it 

 is worthless. 



Every good method for pure culture of aerobes and still more of 

 anaerobes should answei" the following requirements: the colonies 

 must be situated quite free and at due distances from each other 

 on the surface of the solid plates, they must furthermore be readily 

 attainable with the platinum wire. These requirements can only be 

 satisfied by cultivation in ordinary glass boxes or Petri dishes, which 

 may take place in the laboratory by means of the exsiccator method 

 of NovY (see Mace, I.e.). 



After this method, — the best of the chemical ones, — ordinary 

 culture boxes are placed in an exsiccator filled with pure hydrogen 

 and moreover containing some oxygen-removing substance, such as 

 ferro-ferrocyan or alkaline pyrogallol. But this method also has its 

 drawbacks. It is namely impossible quite to prevent the deposition 

 of vapour at the glass covers, so that drops of water falling down 

 come on the plates ; this makes the colonies intermix and spoils the 

 experiment. It is, besides, hardly possible distinctly to see the state 

 of development of the colonies in the closed exsiccator, which may lead 

 to it being opened too early and oblige the experimenter lo begin anew. 

 This is vei-y troublesome considering the complication of the experiment. 



The O'ldium. method has none of these disadvantages, and if 

 well-managed, produces colonies of the anaerobes situated quite free 

 on the surface of the plates and easily reached with the wire. 



The principle of the method is the placing one over the other 

 of two culture plates, separated by a relatively small space of air. 

 One of the plates contains the aerobic microbe which is to absorb 

 the oxygen, while on the surface of the other the anaërobe is to 

 grow. Here, also, I select a definite exam|)le for illustration, namely 

 the strictly anaerobic bacilli of the butyric-acid and the bulyl-alcoholic 

 fermentations; they have corresponding nutrition conditions and may 

 be isolated in the same way. They are spore-producers, thriving best 

 in malt infusion where they cause strong fermentations accompanied 

 with production of hydiogen and carbonic acid. A crude butyric- 

 acid fermentation is prepared as follows. Wheat- or rye-flour, or belter 

 a pap of potatoes infected with soil, is mixed in a glass beaker 



79* 



