314 



tain conditions also accumulate at the centre, nainely then, when all the spirilli to- 

 gether caiinot absorb the total quantity. of oxygen entering along the edge of the pre- 

 paration, and this is indeed easily to be observed, by using a small number of spirilli 

 and a large coverglass. 



So, there is no sufficiënt reason to divide the mobile bacteria into three types 

 according to their relation to free oxygen, as I formerly did, but only into two. It 

 also seems to me that the names for the types, already mentioned, are not quite applic- 

 able, and that it is preferable to call aërophüous all organisms which seek the high- 

 est oxygen tension'), and microaërophilous those which require a lower tension. To 

 this latter group then, belong the obligatous anaërobics as far as now observed, and 

 the aerobic spirilli with regard to their mobility. 



I am obliged here to speak of »aërobic spirilli«, as I have formerly shown that 

 there also exists an obligatous anaërobic spiril, namely the organism of the reduction 

 of sulphates, Spirillum desulfuricans. Though this kind is very mobile, yet the growth 

 is so slow, that I have not succeeded in collecting a sufficiënt number of individuals 

 to get distinct figures of respiration, — a difficulty which exists also more or less 

 with other obligatous anaërobics. 



The conviction that free oxygen is beneficial to all that lives, and in the long run 

 probably even necessary, is based on the relation of the growth of the obligatous 

 anaërobics to this gas, and here the mobile forms as well as those which are not 

 mobile may enter into consideration. Before however describing the experiments 

 which seem decisive, I must fix the attention on the foUowing circumstance. 



For alcohol yeast and the other facultative anaërobics, it must be admitted, that 

 the possibility of their temporary anaërobiosis. is determined by the presence of a 

 provision of oxygen in loose combination with the living matter of the cell itself, by 

 which combination some cell divisions are rendered possible without the supply of new 

 oxygen. Consequently there must be a difïerence between aërated and not aërated cells. 



If it is accepted that this relation holds also good for the obligatous anaërobics, 

 then it is to be expected that their provision of oxygen will be much smaller than 

 that in the yeastcell, so that it is necessary to take much more efficacious measures to 

 render the influence of the oxygen visible in the former than in the latter case. It is 

 therefore desirable, in some cases even necessary, to use for the experiments materials, 

 taken from such cultures as have long been continued in absence of air, by which the 

 provision of oxygen has been lessened. So far as I am now able to judge, strongly 

 aërated anaërobics are, as to their growth, aërophobic, i. e. they grow best there where 

 the oxygen tension is minimum or zero. As contact with air is in itself not sufficiënt 

 to cause aëration, — spores for instance seem less fit to be aërated than vegetative 

 cells, • — there now and then occur strange incidents which make the experiments 

 troublesome. 



The way in which 1 arranged my growth experiments is as follows. 



Malerial of the species to be examined, is introduced, in a not aërated condition, 

 and if possible, in the state of spores, into the culture mass still in fusion, in such a 

 quantity, that the gemis, developped into colonies, may render that culture mass, 

 after solidification, rather opaque. 



') Here is only tiucstion of cxpcrinunts in cumnion air, not in pure o.\ygcn. 



