1886.] On the Multiplication of Micro-organisms. 533 



Again, in another experiment, the following results were ob- 

 tained : — 



Number of Colonies obtained from 1 c.c. 



Description. 



Apr. 14/86. 

 Day of collection. 



Apr. 15/86. 

 Standing 1 day, 

 at 20° C. 



Apr. 17/86. 

 Standing 3 days, 

 at 20° C. 





7 



21 



495,000 





These tables show the enormous capacity for multiplication which 

 is possessed by the micro-organisms present in this deep well-water. 

 This is the more surprising, at first sight, wh-^u it is borne in mind 

 that this water contains the merest trace of organic matter. It must, 

 however, be remembered that this water is at the outset almost wholly 

 free from micro-organisms, and that it has never before been inhabited 

 by such living matters ; it is only reasonable to infer, therefore, that 

 those of its ingredients which are capable of nourishing the particular 

 micro-organisms which flourish in it are wholly untouched, whilst in 

 the case of the river- waters, the most available food supply must have 

 been largely explored by the numerous generations of micro-organisms 

 which have inhabited them. It should also be mentioned that the number 

 of different varieties of micro-organisms is far greater in the case of 

 the river-waters than in the deep well-water, as is at once evident to 

 the naked eye on inspection of a plate cultivation, the deep well-water 

 plates having generally the appearance of a pure culture ; in the 

 latter case, then, the organisms present will probably have a freer 

 field for multiplication than in the presence of competitors, some of 

 which may not improbably give rise to products which are hostile to 

 others. This would also explain the greater capacity for multiplica- 

 tion which we find, as indicated above, in the filtered as compared 

 with the unfiltered river-waters. By the process of filtration the 

 number of different varieties of micro-organisms is largely reduced, 

 as is at once seen by the inspection of the plate cultivations, and 

 those varieties which remain have apparently a more favourable 

 opportunity for reproduction than in the presence of more numerous 

 varieties. 



II. The Multiplication of Pathogenic Micro-organisms. 



The remarkable phenomenon of multiplication which is exhibited 

 by the micro-organisms found in most natural waters obviously leads 

 us to a consideration of the behaviour of parasitic micro-organisms 

 when accidentally introduced, as they frequently must be, into waters 

 of different composition. 



