METHODS OF INVESTIGATING BACTERIA. 



801 



through the upper opening, while a'continuous stream of 

 hydrogen is sent through the lateral tuhe, and when it has 

 passed for a sufficient length of time the tubes are sealed 

 at a and b. In vessels of this kind we ohtain luxuriant 

 growth of the most typical anaerobes. If we wish to 

 obtain the colonies of the anaerobes in such a way that 

 they may be examined under 

 the microscope, we employ 

 little vessels containing a layer 

 of the nutrient material at 

 least 1*5 cm. in depth, and 

 these vessels are placed in an 

 iron case with a tight fitting 

 cover and provided with stop- 

 cocks, by means of which hy- 

 drogen can be passed through 

 the vessel and all the air driven 

 out. For further details, see 

 Liborius, Zcitschr.f. Hygiene, 

 vol. i., part 1. 



If we have to do with bac- 

 teria which will not grow on 

 solid nutrient substrata but 

 only in fluids, the difficulty of 

 isolating them is much greater. 

 This was formerly done by 

 Klebs' method the so-called 

 method of fractional cultiva- 

 tion ; in this method a vessel 

 is in the first place inoculated 

 and the bacteria are allowed to grow; a small quantity 

 is then taken from the first vessel and introduced into 

 a new nutrient material ; this is again allowed to 

 develop, and the process repeated through a series of 

 cultivations. In this method the cultivations gradually 

 become purer and contain only those organisms which 

 grow most quickly under the conditions present, while 

 the chances of the presence of the more slowly grow- 

 ing organisms become constantly less. This method 

 is, however, not as a rule of much use, because it is not 



51 



Fig. 142. Apparatus for the 

 cultivation of anaerobes. 



Isolation of 

 bacteria in 

 fluid nutrient 

 substrata. 



Fractional 

 cultivation. 



