14 METHODS OF JXVIJSTIGATION 



ilar methods have been used only rarely, but they seem 

 to give satisfactory results (Adler, 1918; Gaarder, 

 1918). 



2. ESTABLISHMENT OF EXPERIMENTAL ANAEROBIC 

 CONDITIONS 



The methods of establishing anaerobic conditions in 

 the laboratory form the basis of all experimental work in 

 the study either of the resistance to lack of oxygen or 

 of anaerobic metabolism. Theoretically there are two 

 w^ays of inducing anaerobic conditions, one is to inhibit 

 the processes of aerobic oxidation, the other to remove 

 the oxygen from the medium. 



A. Inhibition of aerohic reactions. One may inhibit 

 aerobic metabolism in an organism by poisoning the mech- 

 anism of aerobic respiration. Obviously, if all the reac- 

 tions utilizing oxygen could be eliminated by this means 

 and if the animal would still survive, it could do so only 

 by virtue of anaerobic processes. Several substances, 

 like hydrocyanic acid, sodium azide or carbon monoxide, 

 can be used to inhibit aerobic respiration and it is surpris- 

 ing how resistant many invertebrates are to these poisons. 



Nevertheless it is not possible in this way to arrive at a 

 purely anaerobic metabolism. The different available 

 poisons interrupt at various points the chain of aerobic 

 processes, but no single substance or combination of va- 

 rious poisons inhibits all the reactions which utilize mole- 

 cular oxygen. As a rule, a certain, though sometimes 

 quite small, residual oxygcni consumption remains. 



The use of poisons can consequently not be recom- 

 mended for a study of the resistance of organisms to the 

 lack of oxygen or of similar problems. Such poisons 

 are nevertheless helpful tools, and when used conjointly 

 wdth those that act on the anaerobic part of the metab- 

 olism (like iodo-acetic acid, iodo-acetamide and others) 

 they give an inside view into the mechanism of anaerobic 

 life that cannot be obtained by other means. So far, in 



