72 PLANT RESPIRATION 



Each time care is taken that the middle bulb is entirely filled 

 with acid. Then the experiment is begun. The gas now 

 includes so httle air that after the absorption of loo cc. of 

 carbon dioxide with caustic potash [in a eudiometer] there 

 remains a small bubble of air scarcely visible to the naked eye. 

 For most investigations such an insignificant amount of air 

 is of no account. 



A vacuum has seldom been used to provide anaerobic condi- 

 tions of hfe. Nabokich^ placed the research material in a 

 vacuum flask and exhausted the flask with a strong air pump to 

 a mercury pressure of 0.25 mm. It must be pointed out that 

 with this method the material is placed under an extraordinary 

 physical condition which cannot possibly fail to afTect the experi- 

 mental results. 



It would be entirely inadmissible to be content with immersion 

 of the experimental material in water or various dilute solu- 

 tions. It has already been pointed out [p. 59] that strongly 

 aerobic plants pro\dded with powerful oxidising enzymes 

 respire normally even under water and there obtain oxygen in 

 sufficient quantity. It is also absolutely insufiicient for accu- 

 rate experiments to immerse the material in water or dilute 

 solutions and to cover the surface of the water with a fluid in 

 which oxygen is insoluble. It is impossible by this method to 

 isolate entirely the experimental material from the atmospheric 

 oxygen. On the other hand, it is satisfactory to dip in water or 

 certain nutrient solutions plants which are rapidly killed by 

 anaerobic conditions, and then to replace the air in the con- 

 tainer with an inert gas. This measure tones down the poison- 

 ing of the experimental material, since the toxic products of 

 the anaerobic metaboKsm diffuse out into the solution. 



It has already been pointed out that it is often of interest 

 to carry out quantitative determinations of alcohol in the case 

 of studies of anaerobic respiration. A qualitative demonstration 

 of ethyl alcohol is also often of great importance. To prevent 

 a loss of the alcohol in experiments with a gas current, a wash 

 bottle set in melting ice and filled with distilled water is inter- 



1 Nabokich, A. Ber. d. bot. Ges. 19: 222. 1901; 21: 398, 467. 1903; Beih. z. bot. 

 Centralbl. 13: 272. 1903. 



