456 Sir H. E. Roscoe and Mr. J. Lunt. [Apr. 23 r 



and bacteriological, of the two marked changes which sewage is liable 

 to undergo, i.e., on the one hand purification, or the gradual destruc- 

 tion of putrescible matter without the formation of offensively smell- 

 ing products, and on the other putrefaction. It was desired to 

 ascertain which organisms are concerned in the first of these processes 

 and which in the second, as likewise to gain an insight into 

 methods by which such changes are effected. 



For all the organisms described, the authors have determined tl 

 absorptive power for free oxygen when cultivated in a perfectly pure 

 state, and also for which of the organisms free oxygen is a necessity 

 of their activity and growth. 



Each organism has been examined as to its power of growth in 

 liquid medium from which every trace of free oxygen, both 

 and dissolved, has been rigorously excluded. 



It is shown that anaerobic organisms associated with putrefactioi 

 although able to grow in complete absence of oxygen, yet when that 

 gas is present are able to absorb it rapidly, and thus prepare the con- 

 ditions for their anaerobic growth. 



The following methods for the isolation of micro-organisms ha 

 been used : 



(1.) The method of gelatine plate-culture. 



(2.) A method, fully described, for the isolation and cultivation 

 anaerobic organisms. 



(3.) A method for the isolation of spore-forming organisms. 



(4.) The dilution method. 



The method used for the isolation of anaerobic organisms coi 

 in their cultivation in a specially devised form of flask contaii 

 sterile nutrient broth, through which liquid could be passed a stream 

 or pure hydrogen, freed fi-om all traces of oxygen by passing ove 

 glass beads, in two Emmerling's tubes, moistened with alkaline j 

 gallate. 



As the authors have shown in a previous paper (' Chera. 

 Journ.,' 1889, Trans., p. 554), this treatment frees the liquid coi 

 pletely from dissolved oxygen. 



Crude sewage was carried through three cultivations in pi 

 hydrogen, when it was found that not only had all aerobic organis 

 been eliminated, but only one form of anaerobic organism appeal 

 viz., Proteus vulgaris, and this method may be used for its isolation. 

 Several other organisms, although isolated by different methods 

 the above, were found to grow in the pure state in nutrient broth 

 from which all traces of free oxygen had been excluded. These ai 

 fully described in the paper. 



In the method for the isolation of spore-forming organisms, all 

 others were eliminated by heating the sterile broth, in which 

 sowing had been made from crude sewage, to 80 C. for ten minutes. 



