( 14 ) 



in a system of bright and dark lines, as soon as the brightness in 

 the neighbourhood of tlie lines is not perfectly symmetrical with 

 respect to their centres. 



At any ratc! we may conclude from what precceds that wo cannot 

 be too critical while observing maxima and minima of brightness, 

 and that in many cases we shall even have to convince ourselves 

 of the existence or non-existence of real maxima and minima of 

 brightness corresponding to the observed maxima and minima. 



Bacteriology. — On the. relation of the ohlujutoas anaërobics to 

 free oxijcjen. By Prof. M. W. Beijerinck. 



The relation of the living cell to free oxygen is best to be judged 

 from the influence of this gas on the growth and on the mobility. 

 Of course, only the first method is of universal application. 



As to the mobile microbes, some time ago I gave the name of 

 „figures of respiration" ^) to the peculiar groupings, which originate 

 in preparations destined for the microscope, in consequence of the 

 access of oxygen only along the edge of the examined drop under 

 the cover-glass, the microbes being thereby enabled to seek that 

 quantity of oxygen which is best adapted to their respiration. Three 

 types may here be distinguished according as the microbes seek the 

 highest tension of the oxygen along the edge, a middle tension at 

 some distance of it, or the smallest tension in the centre of the 

 preparation. These types I called the aerobic, the spirillous and the 

 anaerobic type. 



Further experience has shown that the anaerobic type, charac- 

 terised by the accumulation of the moving microbes at that spot 

 of the preparation where the oxygen tension is minimum, — com- 

 monly near the centre, — does not exist as a special type, but 

 becomes visible only under particular circumstances, and further, 

 that when the aeration of the preparation is sufficiently small, all 

 anaërobics, examined till now, appear to belong to the spirillous 

 type, that is to say, they not only don't fly those places in the 

 preparation, where a small oxygen tension still exists, but they even 

 seek them. 



This tension, beneficient for the anaërobics, is however very slight, 

 whence follows, that by using only a moderate number of microbes, 

 consuming but very little oxygen, there may enter at tlie edge more 

 oxygen than is wanted. In such a case the tension, most approaching 



1) Centralblatt fur Bacteriologie Bd. U pag. 837, 1893. 



