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that the microaeropbily grows indistinct, without changing into 

 aërophily. 



Recapitulating, and adding some instances not yet mentioned, I 

 come to this conclusion : 



Jërophilous are: All aerobic bacteria (except some spirilli), most 

 facultative anaërobics, probably all cells of higher animals and plants, 

 most infusoria. 



Microal'rophilous are: The few hitherto examined ohligatous 

 anaërobics, to which belong also the chromatia and other sulphur- 

 bacteria, and Spirillum desulfuricans. Of the facultatives probably 

 all lactic ferments, besides some (perhaps many) species of monads, 

 and some infusoria. 



Ai'ropliilous ivith regard to c/roicth, niicroacrophilons tvith regard 

 to motion are/ Some true spirilli, perhaps also some monads. 



Though nobody will be surprised that, in reason of the above 

 observations, I believe that all living organisms known at present, 

 require free oxygen for their existence, I am far from pretending to 

 have furnished the entire proof for that belief. It may even be asked 

 whether there is cause to speak of „want" of free oxygen, and if 

 „use of it if accessible" were not more adequate. 



With regard to the examined obligatous anaërobics I have only 

 shown that an extremely small quantity of free oxygen is propitious 

 to their growth and mobility, but not yet that in the long run they 

 would perish without it i). 



I must however insist on this being positively the case with the 

 aërophilous facultative anaërobics, such as alcohol ferments, B. coli 

 comnnme, etc. If these are prevented from laying in a „provision" 

 of oxygen, on which to live when this gas fails, the growth soon 

 ceases and, even with the best food, life too*). This fact is very 

 singular, for the extremely small quantities here concerned, are 

 nothing as to the development of energy. 



Consequently it is not clear why the combined oxygen, which 

 abounds in the food, cannot here fill the place of free oxygen. With 



1) Experiments in this latter direction have not yet given any sure results and 

 have only proved that, with apparently efficacious precautions, anaërobiosis without 

 access of air can long go on. So I could, without supply of air, make seven butylic 

 fermentations go on successively, but at the seventh there arose some doubt whether 

 the bacteria had varied or that an infection from without with butyric ferment had 

 occurred. 



2) For this reason I formerly proposed to call these organisms //temporary anaëro- 

 bics", but now that I am more and more convinced that also the //obligates" can 

 exist only temporarily without free oxygen, I no more attach much value to that term. 



