194 MICRO-ORGANISMS IN WATER 



motile or not, whilst their power of multiplication 

 would also depend upon the particular forms present, 

 and upon their vital activity. As a matter of fact, in 

 some cases a subsequent redistribution of the organisms 

 was found to take place, and in others not. 



The following are some of the principal results 

 obtained in these investigations : — 



Agitation with spongy iron. — The water was shaken 

 with one-tenth of its weight of this material for fifteen 

 minutes. The water was allowed to subside for half- 

 an-hour before examination. 



Bacterial Purification of Water by means of Agitation and 

 Subsidence (Percy Frankland, 1885) 

 Untreated water contained 609 micro-organisms in 1 c.c. 

 After 15 minutes' agitation 

 with spongy iron and 

 30 minutes' subse- 

 quent subsidence . 63 „ „ 

 Reduction in the number of micro-organisms = 90 per cent. 



Again, in another experiment : 



Untreated water contained 155 micro-organisms in 1 c.c. 

 After 15 minutes' agitation 

 with (Spongy iron and 

 30 minutes' subse- 

 quent subsidence . 10 ,, „ 

 Eeduction in the number of micro-organisms = 93 per cent. 



Agitation with chalk. — Water was shaken for fifteen 

 minutes with one-fiftieth of its weight of chalk, and 

 then allowed to subside for five hours : — 



Untreated water contained 8,000 micro-organisms in 1 c.c. 

 After 15 minutes' agitation 

 with chalk and 5 

 hours' subsequent sub- 

 sidence . . . 270 ,, „ 

 Eeduction in the number of micro-organisms = 97 per cent. 



Agitation with animal charcoal. — The same water as 

 that used in the last experiment was shaken with one- 

 fiftieth of its weight of animal-charcoal for fifteen 



