( 15) 



the required optimum, will be found in the centre. The accumu- 

 lation of the microbes will then also be localised to the centre, 

 causing' the semblance of an anaerobic type as a special case. It is 

 clear, that if this is the right explication, the true representatives 

 of the second type, viz. the spirilli, must under certain conditions 

 also accumulate at the centre, namely then, when all the spirilli 

 together cannot absorb the total quantity of oxygen entering along 

 the edge of the preparation, and this is indeed easily to be observed, 

 by using a small number of spirilli and a large coverglass. 



So, there is no sufficient 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 mo that the 

 names for the types, already mentioned, are not quite applicable, and 

 that it is preferable to call aërophilous all organisms which seek the 

 highest oxygen tension ^), and microacrophilous those which require 

 a lower tension. To this latter group then, belong the obligatous 

 anacrobics as far as now observed, and the acTobic spirilli with 

 regard to their mobility. 



I am obliged here to speak of „aerobic spirilli", as I have for- 

 merly shown that there also exists an obligatous anaerobic spiril, 

 namely the organism of the reduction of sulphates, Spirillum desul- 

 furicans. Though this kind is very mobile, yet the growth is so 

 slow, that I have not succeeded in collecting a sufficient 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 fjrowth 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 hoM-ever describing the experi- 

 ments which seem decisive, I must fix the attention on the following 

 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 oxi/gen in loose com- 

 bination with the living matter of the eel! itself, by which combination 

 some cell divisions are rendered possible without the supply of new 

 oxygen. Consequently there must be a difference between aerated 

 and not aerated cells. 



1) Here is only question of experiments in common air, not in pure oxygen. 



