ORIGIX OF AXAEROBIOSIS 273 



of oxygen accompanying an increasing complexity of 

 chemical and morphological organization. 



"4. This increase in need of oxygen, as complexity 

 increases, is paralleled in the growth of the individual 

 organism, the ability to endure complete abstraction of 

 oxygen varying inversely with age and size. 



"5. The oxygen of the atmosphere appears to have 

 been formed exclusively by plant action. In the be- 

 ginning there was probably no oxygen free: if there 

 had been any, it would have been very quickly absorbed 

 by the unoxidized substances of the earth's crust or the 

 quantity would have been so small as to be practically 

 negligible." 



Since Snyder wrote his article some new information 

 has become available on several of the points he dis- 

 cusses, and, though we look ui3on his paper as a stimulat- 

 ing piece of work, we find ourselves in disagreement with 

 most of his statements. 



To i^oint 1 : Whether the simplest forms of life are 

 still anaerobic is a debatable matter. According to Sny- 

 der they are represented by the anaerobic bacteria, but, 

 to the writer's knowledge, no generally accepted phylo- 

 genetic relationship of the various groups of bacteria has 

 been established as yet. As to the statement that the ma- 

 jority of lower organisms can live more or less con- 

 tinuously under anaerobic conditions, our review^ con- 

 stitutes sufficient proof to the contrary in so far as the 

 animals are concerned. 



To point 3 (in part) : The assumption that an increas- 

 ing complexity in morphological organization increases 

 the need for oxygen is contradicted by the fact that 

 amongst protozoa the strictest anaerobes are found 

 amongst the most specialized and complex forms, for 

 example, the sapropelic and rumen ciliates. In no phy- 



1. Part I, Chapter III. 



