1889.] Carbonic Anhydride, fyc., on Micro-organisms. 293 



In my experiments I used the ordinary methods of plate-cultivation 

 (Esmarch's important modification having not yet been published), 

 the plate-cultivations of the various micro-organisms being then sub- 

 mitted to an atmosphere of different gases in the following manner : 

 A suitable attenuation of a particular micro-organism was employed, 

 and gelatine plates were poured in the usual way; the different plates, 

 resting one above the other on small glass stages, were placed in a flat 

 porcelain dish and covered over with a glass bell-jar. Mercury was 

 then poured into the dish, thus forming an effectual seal, and sterilised 

 water was poured on to the surface of the mercury. The weight of 

 the bell-jar causes it to sink to a certain depth into the mercury, so 

 that the damp-chamber is in reality cut off from the external air by 

 the mercury, and not by the sterilised water. A piece of sterilised 

 india-rubber tubing is then introduced beneath the mercury, and a 

 current of any particular gas can be passed into the chamber, the 

 excess of gas escaping at the edge of the bell-jar through the mercury 

 and water. 



After the air has been driven out of the chamber in this manner, 

 and replaced by any given gas, the tubing is removed, and the dish is 

 kept at the requisite temperature, which in my experiments was 

 about 20 C. 



The particular micro-organisms which I used in these experiments 

 were (1) the Bacillus pyocyaneus, (2) Koch's Comma Spirillum, 

 (3) Finkler's Comma Spirillum, which were procured from the 

 Hygienic Institute in Berlin. The different organisms were obtained 

 in a suitable degree of attenuation by mixing them with sterilised 

 water, from which a definite quantity was taken and gelatine plates 

 poured. 



In each experiment one plate was placed in a damp- chamber con- 

 taining ordinary air, whilst a second was exposed in a similar chamber 

 filled with the particular gas under examination. After the lapse of 

 an adequate period of time admitting of their development, the 

 colonies were counted in both cases and the results compared. 



I. Experiments With Hydrogen. 



The hydrogen was generated in a Kipp's apparatus by the action of 

 dilute sulphuric acid on zinc; it was purified by passing it through a 

 saturated solution of caustic soda, and was then conveyed through a 

 sterilised piece of india-rubber tubing and a sterile plug of cotton- 

 wool into the damp-chamber containing the inoculated gelatine 

 plates. The following results were obtained in the use of this 



