300 Carbonic Anhydride and Micro-organisms. [Jan. 24, 



Nitrons oxide acts, therefore, upon these three micro-organisms 

 much in the same manner as carbonic oxide. 



Remarks. 



From the above series of experiments, it is at once apparent that 

 the four different gases act very differently towards micro-organisms. 

 Of the four gases employed, hydrogen, carbonic oxide, nitrous oxide, 

 and carbonic anhydride, hydrogen had the least deleterious effect 

 upon those microbes with which I experimented, whilst carbonic 

 anhydride had the most destructive influence. There is, therefore, no 

 longer any doubt, as indeed Liborious and C. Frankel have already 

 pointed out, that in the anaerobic culture of micro-organisms hydrogen 

 is by far the most suitable medium for the expulsion of air, whilst 

 carbonic a,nhydride, owing to its markedly deleterious eftect upon 

 many forms of bacteria, is not only ill suited, but is in many cases 

 quite unfit for such a purpose. 



And although there is no doubt, as Buchner asserts, that all those 

 bacteria which give rise to fermentations attended with an abundant 

 evolution of carbonic anhydride, must also be capable of nourishing 

 in an atmosphere of this gas, yet it by no means follows that these 

 organisms attain their full vitality in such an atmosphere. On the 

 contrary, it is very possible that their anaerobic and fermenting 

 powers only reach their maximum degree of activity when the gaseous 

 products to which they give rise are removed either by a really 

 indifferent gas, such as hydrogen, or by a vacuum. 



The results of some experiments on the fermentative activity of 

 yeast by JBoussingault (' Compt. Rend.,' vol. 91, p. 37) support this 

 view, for they show that in such a vacuum alcoholic fermentation 

 takes place more actively, and is more quickly completed than at the 

 ordinary pressure of the atmosphere. 



As regards the particular behaviour of these three micro-organisms 

 towards carbonic anhydride, the results of my experiments agree 

 almost entirely with those of Frankel. In both series of experiments 

 ft was found that the growth of B. pyocyaneus was entirely suspended 

 by the action of this gas, but that on subsequent exposure to air the 

 growth, attended with the formation of the characteristic pigment, 

 commenced. 



Again, in both series of experiments, it was observed that carbonic 

 anhydride completely arrested the growth both of Koch's comma 

 spirillum and Finkler's spirillum, but whilst C. Frankel always 

 succeeded on subsequent exposure to the air in obtaining a growth, 

 although a very feeble one, in my experiments no such secondary 



srowth was observed. 



o . , 



This discrepancy may, however, very possibly arise from the differ- 

 ence in the power of resistance which is often observed in the same 



