196 BACTERIOLOGY. 



media, but, owing to its usual small capacity, gives 

 better results with fluid media. (For precautions in 

 using hydrogen see note to Frankel's method, page 

 198.) 



Method of Buchner. The plan suggested by Buchner 

 of allowing the cultures to develop in an atmosphere 

 robbed of its oxygen by pyrogallic acid gives very good 

 results. In this method the culture, which is either a 

 slant- or stab-culture in a test-tube, is placed — tube, 

 cotton plug, and all — into a larger tube in the bottom 

 of which have been deposited 1 gramme of pyrogallic 

 acid and 10 c.c. of y^- normal^ caustic potash solution. 

 The larger tube is then tightly plugged with a rubber 

 stopper. The oxygen is quickly absorbed by the pyro- 

 gallic acid, and the organisms develop in the remaining 

 constituents of the atmosphere, viz., nitrogen, a small 

 amount of COg, and a trace of ammonia. 



Method of 0. Frdnkel. Carl Frankel suggests the 

 following as a modification of or substitute for the tubes 

 of Liborius: the tube is first inocidated as if it were 

 to be poured as a plate or rolled as an ordinary Esmarch 

 tube. The cotton plug is then replaced by a rubber 

 stopper, through which pass two glass tubes. These 



1 A normal solution is one that contains in a litre as many grammes of the 

 dissolved substance as are indicated by its molecular equivalent. The equiv- 

 aleut is that amount of a chemical compound which possesses the same 

 chemical value as does one atom of hydrogen. For example : one molecule 

 of hydrochloric acid (HCl) has a molecular weight and also an equivalent 

 weight of 36.5; a molecule of this acid has the same chemical value as one 

 atom of hydrogen. Its normal solution is therefore 36.5 grammes to the litre. 

 On the other hand, sulphuric acid (H2SO4) contains in each molecule two re- 

 placeable hydrogen atoms ; its normal solution is not, therefore, 80 grammes 

 (its molecular weight) to the litre, but that amount which would be equiva- 

 lent chemically to one hydrogen atom, viz. , 40 grammes (one-half its molecu- 

 lar weight) to the litre. A normal solution of caustic potash contains as 

 many grammes to the litre as the number of its molecular weight— 56.1 

 grammes to the litre of water. 



