1889.] Carbonic Anhydride, fyc., on Micro-organisms. 295 



air-plates, and they did not exhibit the characteristic depression on 

 the surface of the gelatine. 



2nd Experiment (March 29th, 1886). 



Air-plates H-plates 



(after 4 days) . (after 1 days) . 

 Number of colonies from 1 c.c. 



of the mixture 100 110 



The vitality of Koch's comma spirillum is therefore in no way 

 affected by exposure to an atmosphere of hydrogen, although its 

 development into colonies is considerably retarded. 



(c.) With Finkler's Spirillum. 

 1st Experiment (March 15th, 1886). 



Air-plates H-plates 



(after 4 days) , (after 7 days) . 

 Number of colonies from 1 c.c. 



of the mixture 12,107 6726 



The colonies on the hydrogen-plates had the appearance of small 

 milky dots, and caused in many cases a depression on the surface of 

 the gelatine ; they resembled, in fact, very young colonies on an ordi- 

 nary plate culture of these spirilla. 



In an atmosphere of hydrogen it would appear that of the three 

 organisms with which I have experimented Koch's comma spirilla 

 were the least prejudicially affected in their vitality. 



II. Experiments with Carbonic Anhydride. 



The gas was prepared in a Kipp's apparatus by the action of dilute 

 hydrochloric acid on marble, and purified by passing it first through a 

 saturated solution of carbonate of soda and then through a sterilised 

 plug of cotton-wool. 



The same three micro-organisms were submitted to experiment in 

 the manner previously described. 



(a.) With the B. pyocyaneus. 

 1st Experiment (March 4th, 1886). 



Air-plates CO 2 -plates 



(after 2 days). (after 9 days). 



Number of colonies from 1 c.c. f 22,412 "I Q # 



of the mixture 1 22,651 J 



*This plate was then placed in a damp-chamber in an atmosphere 

 of air, and after seven days 2023 colonies were found. 



