LIFE WITHOUT OXYGEN 109 



to show that, in the case of certain forms supposedly anaerobic, 

 for example the butyric acid ferments, the minutest trace of 

 oxygen sufficed during a long series of generations. Beijerinck, 

 therefore, proposed to divide living organisms into two classes 

 — those which thrive best when the oxygen tension is at a 

 maximum and those which thrive best when it is at a very low 

 tension. The former he called aerophile, the latter micro- 

 aerophile. This conception seemed to fit the facts so well that 

 it was generally accepted for a time by the most careful observers, 

 among them Fermi, A. Fischer, Chudiakow and others. 1 But 

 the discovery and investigation of the light-producing or photo- 

 bacteria revealed a test for the presence of oxygen of such 

 sensitiveness as to disclose the most minute trace. With the 

 aid of this last and the development of a technique of quite 

 extraordinary refinement, it has been possible, notably through 

 the researches of Omelianski, Burri and latterly by the decisive 

 work of Kiirsteiner, 2 to establish the correctness of Pasteur's 

 early observations. 



To those to whom the law of continuity or curve of proba- 

 bilities is a constant mental companion, this final demonstration 

 seemed a foregone conclusion. The fact that in passing from 

 organisms like the higher animals to which a constant supply of 

 oxygen is a necessity, every gradation in the need of oxygen was 

 to be met with down to a point at which the utmost refinement 

 of technique was required to discover that it was of use at all, 

 left little reasonable doubt in the philosophic mind that beyond 

 this point the absolute anaerobe must exist. 3 



Why now should we regard these anaerobic bacteria as the 

 lowest, the most primitive and therefore in all probability the 

 earliest of all living organisms known ? For very much the same 

 reason that we speak of the plant as " lower " in the scale of life 

 than the animal. In general, at least, the higher types of animals 

 are able to exist only by means of preformed organic products. 

 The plant is able to derive its food directly from the soil and 

 the air. It is evident therefore that a great land flora must have 

 preceded any notable development of a land fauna. 



Further, it is known that prior to the development of an 



1 For full literature, cf. Omelianski, in Lafar, Handb. d. tech. Mycol. 2nd 

 edition, vol. ii. 576, 1907. 

 3 L.c. with full literature. 

 3 For a full discussion, cf. Euler, Pflanzenchemie, vol. ii. p. 152 ff. 



