REPLACING THE AIR BY A HYDROGEN ATMOSPHERE 151 



The Stick Culture Method. Anaerobic cultures may be raised in 

 stick cultures. For this purpose it is well to have a somewhat longer 

 tube containing instead of 10 c.c., 15 to 20 c.c. of the culture medium. 

 To the latter, when used to raise anaerobic stick cultures, a reducing 

 substance, such as sugar, or, still better, formate of sodium, is often 

 added. Anaerobic stick cultures can also be made as follows : A culture 

 tube containing the usual amount of medium is inoculated as a stick 

 culture. The medium in a second tube is melted and allowed to 

 cool to near its point of solidification. Before this is reached, however, 

 the cotton plug and the upper end of the tube are flamed, the former 

 removed and the still fluid contents of the tube poured into the stick 

 culture in the first tube. The added medium will successfully exclude 

 the air from the lower inoculated strata, giving the anaerobic germ a 

 chance to grow. 



Exclusion of Air from Fluid Media. A simple and often successful 

 method of raising anaerobic germs in fluid media (bouillon, milk, etc.) 

 is the following: The media, shortly before use, are subjected to a 

 prolonged boiling, which drives out the atmospheric air. The culture 

 flasks without being in any way disturbed or agitated, which would 

 again mix the culture medium with atmospheric air, are allowed to 

 cool, and are then at once inoculated. In the meantime there should 

 be prepared some oil, vaselin or paraffin of a low melting point, which 

 has been sterilized by heat and allowed to cool. As soon as the culture 

 flasks have been inoculated some of the oil, vaselin or the like is 

 poured into them. These substances, lighter than water, will float on 

 the surface and exclude the culture medium and the anaerobic bacteria 

 contained therein from contact with the atmospheric air. 



Replacing the Air by a Hydrogen Atmosphere. Anaerobic bacteria 

 can be raised both in an atmosphere of hydrogen and in one composed 

 of nitrogen from which all oxygen has been removed. When the 

 ordinary air is to be replaced by hydrogen it is necessary to use an 

 apparatus developing a continuous current of this gas. The simplest 

 and safest device of this kind is a Kipp gas generator. It consists of 

 two glass globes (A and B) joined together by a narrow neck and 

 resting on a base. The upper globe (^4) possesses a lateral tubular 

 outlet ( T) closed with a perforated rubber stopper which is provided 

 with a glass tube and a stopcock (ST). A third globe (C) is generally 

 shaped like a separatory funnel with a narrow conical glass tube 

 fitting air-tight into the neck (N) of the upper globe (^4) without 

 completely closing the passage between the two jointed globes at (M ). 

 When this apparatus is to be used for the generation of hydrogen, 

 the rubber stopper with the gascock at ( T) is removed and pieces of 

 broken glass are introduced in such a manner that they collect around 

 the long glass tube in A. Next granulated zinc is introduced into 

 globe A in the same manner. The zinc, provided that the broken 

 glass has been arranged properly, cannot fall into B. The next step 

 is to open the stop-cock at ST and fill B through the upper globular 



