1 2 Biological Relation Between Bacteria and the More 



2. The disappearance of the micro-organisms which 

 grow on gelatine media in polluted streams takes place 

 during the day as well as night, and is not influenced by 

 light, though sunlight seems to assist in killing off the 

 bacteria. . . . : , 



3. The death of micro-organisms follows rapidly, and 

 during the course of twenty kilometers, requiring about 

 eight hours, 50 per cent of the germs disappeared. 



Undoubtedly, the facts as presented by this thorough 

 and practical investigation can be interpreted in several 

 different ways. In the first place, it must be borne in 

 mind that the nitrifying bacteria, those which are con- 

 cerned most particularly in the purification of polluted 

 waters, do not grow on the ordinary gelatine media : con- 

 sequently these did not enter into the consideration of the 

 bacteriological analyses made by these investigators. In 

 the second place, through the action of sedimentation, some 

 of the organic matter subsided and took its place on the 

 bottom of the river; with the subsidence of the food 

 material for the micro-organisms it is most evident that 

 they also took the same course ; so that in this manner a 

 considerable proportion of the micro-organisms may have 

 been removed. Furthermore, it is altogether probable 

 that there was, and always is, a marked reduction of those 

 bacteria which are capable of growing on gelatine media, 

 and that they are destroyed through the purifying agencies 

 at work in flowing streams. 



The putrefactive decomposition of 'albuminous material 

 of animal and vegetable origin is effected by a great 

 variety of micro-organisms and gives rise to the formation 

 of a great variety of products, some of which are volatile 

 and characterized by their offensive odors. According to 

 Fliigge, the first change which occurs consists in the trans- 

 formation of the albumens into peptone, and this may be 

 effected by a large number of different bacteria. The 

 special products of putrefaction vary according to the 



