CHAPTER II 



BASIS FOR THE DIFFERENCES IN ANAEROBIC 

 FUNCTIONS AMONG INVERTEBRATES 



We shall discuss here the three following problems: 



(1) Why is oxygen injurious to anaerobic invertebrates'? 



(2) Why cm some organisms be deprived of oxygen, 

 while others cannot? and (3) How is auaerobiosis related 

 to oxidation-reduction potentials? 



1. WHY DOES OXYGEN INJURE ANAEROBIC INVERTEBRATES? 



Regardless of whether future investigation will show 

 that the protozoa of the group A in our classification are 

 strictly anaerobic, or utilize oxygen when they have 

 access to it, or even require traces of that gas, the fact 

 remains that they are injured at least by higher concen- 

 trations of oxygen. The question as to the immediate 

 cause of this injurious action has been studied primarily 

 by bacteriologists. Jahn (1941) has recently summarized 

 their findings and discussed to what extent these can be 

 applied to protozoa. 



He mentioned the following theories: 1. Oxj^gen is it- 

 self toxic; 2. Anaerobes do not contain catalase and are 

 therefore not capable of destroying the toxic hydrogen 

 peroxide which is formed under the action of oxygen; 



3. The growth of anaerobes is dependent upon the pres- 

 ence of a low oxidation-reduction potential in the me- 

 dium, the attainment of which is prevented by oxygen; 



4. Oxygen forms a loose chemical complex with the res- 

 piratory system of obligatory anaerobes, and thereby 

 inhibits its activity. 



According to Jahn there is little evidence for the first 

 two theories; though, of the two, he prefers the second 

 for explaining th(^ principle of Cleveland's (1925, 1925b) 

 method of eliminating parasitic protozoa from a variety 

 of hosts by oxygenation. The second theorv has also 



