321 



difticult aiul suijject to doubt. It sown, however, iii a proper solid culture mass, to 

 which calcium carboiiate is added, in a deep experiment-tube, it may be observed 

 Ihat, under favorable circumstances, at a certain depth below the surface, the tor- 

 mation of acid is the most vigorous. This is caused by the existence of a niveau, 

 very rich in bacteria if compared with deeper layers where less, as well as with those 

 nearer to the surface, where more oxygen is present. After sonic time, however, so 

 many colonies originate, as well at the surface as in the deptli, that the niicroaëro- 

 phily grows indistinct, without changing into aërophily. 



Recapitulating, and adding some instances not yet mentioned, I conie to this con- 

 clusion: 



Aërophiloiis are: All aerobic bacteria (e.xcept some spirilli), most facultative 

 anaërobics, probabiy all cells of higher animals and plants, most infusoria. 



Microa'érophilous are: The few hitherto examined obligatous anaërobics, to which 

 belong also the chromatia and other sulphurbacteria, and Spirilliim desulfuricans. 

 Of the facultatives probabiy all lactic ferments, besides some (perhaps many) species 

 of monads, and some infusoria. 



Aërophilous ivitli regard to growth. microaërophilous with regard to motion 

 are: Some true spirilli, perhaps also some monads. 



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

 lieve that all living organisms known at present, require free o.xygen for their exi- 

 stence, 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 must however insist on this being positively the case with the aërophilous fa- 

 cultative anaërobics, such as alcohol ferments, B. coli commune, 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 coticerned. are nothing as to 

 the development of energy. 



Consequently it is not clear why the combined oxygen, which abounds in the 

 food, cannot here fiU the place of free oxygen. With the unknown signification of the 

 latter it is, to be sure, quite uncertain whether there must exist a minimum limit 

 beneath which the possibility of life is totally excluded; but as this limit does certainly 

 exist fort the facultatives, one is by analogy inclined to accept its existence every- 



') Experiments in this latter direction have not yet fjiven any sure rcsults 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 sevcn 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. 



-) For this reason I formerly proposed to call these organisms «teinporary anaë- 

 robics», but now that I am more and more convinced that also the »obligates« can 

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



M. \V. Beij er i nek, Verzamelde Geschriften; Derde Deel. 21 



