ANAEROBIC RESPIRATION 7 1 



the only one to use nitrous oxide. More detailed accounts of 

 these experiments are to be found in Moeller's original paper. 

 Carbon dioxide has even been used in some cases to provide 

 an atmosphere free from oxygen. Carbon dioxide is not an 

 inert gas and may be used only for special problems. Such is 

 the case, for example, if the liberation by anaerobic respiration 

 of gases other than CO2 is being tested.^ Such experiments 

 must be of short duration or the material is injured by the carbon 

 dioxide.' It is best to pass a current of carbon dioxide through 

 the plant container until the air is completely displaced, and 

 then to close off the container. After closing the experi- 

 ment, the gases are displaced from the container by a current of 

 carbon dioxide into a eudiometer filled with concentrated caustic 

 potash solution, where the CO2 is absorbed and any other 

 gases remain in high concentration. The residue not absorbed 

 by lye can now be analysed. It is evident that only strictly 

 pure carbon dioxide can be used for these experiments. It can 

 best be produced by heating chemically pure sodium bicarbon- 

 ate in a combustion tube. Very pure carbon dioxide is obtained 

 by the action of a dilute solution of sodium bisulphate on a 

 coarsely pulverized fusion of sochum carbonate and potassium 

 carbonate.- It is scarcely possible to obtain carbon dioxide 

 free of air by the use of marble and hydrochloric or sulphuric 

 acid. The following method of procedure reduces this contami- 

 nation with air to a minimum. Well-boiled marble in small 

 pieces the size of peas is used in the solution of hydrochloric 

 acid, which is made up with distilled water. The middle bulb 

 of a small Kipp generator is entirely hlled with such pieces of 

 marble and the air is displaced from the apparatus in the follow- 

 ing manner. By opening the stopcock the middle bulb is 

 rapidly filled with the acid and then the stopcock is suddenly 

 closed. The Hquid is thereby forced into the upper bulb by the 

 carbon dioxide. This operation is repeated three or four times. 



1 Kostytschew, S. Ber. d. bot. Ges. 24 : 436. 1906:25: 178. 1907- 



2 Bornttager, H. Z. f. analyt. Chem. 29: 140. 1890. 



<* A very marked exception to this rule is the increased growth of anaerobic 

 bacteria, such as Bacillus nrlchii, B. telani or B. Bolulinus, when exposed in tube 

 cultures to increased tensions of CO2. This behaviour is reported by Rockwell, 

 G. E. Jour. Infect. Diseases 35:581-586. 192^— Ed. 



