18 BACTERIOLOGICAL EXAMINATION OF WATER. 



of B. prodigiosus, M. candicans, M. staphylococcus anreus, M. 

 staphylococcus albus, or B. typhosus, after shaking by hand or 

 in an apparatus. The growth of B. violaceus, however, seemed 

 to be restrained, and the liquefaction produced by Sp. Finkler 

 Prior appeared to be slower. Meltzer concluded from his 

 researches that many bacteria were killed by strong shaking in a 

 machine, while others remained alive and multiplied. 



From these observations it is apparent that the movement 

 which micro-organisms in water sustain under ordinary circum- 

 stances has no appreciable influence on their vitality. 



ON THE SEDIMENTATION OF MICRO-ORGANISMS. 



Sedimentation plays a very important part in changing the 

 bacterial contents of water supplies. The effect of subsidence 

 has been investigated by many workers. 



Bolton allowed a tall flask to stand at a low temperature, and 

 then took specimens from the surface, the centre, and the bottom 

 of the flask. The following results were obtained : 



From the surface. From the centre. From the bottom. 



No. of bacteria No. of bacteria No of bacteria 



perc.c. per c.c. per c.c. 



First specimen after \ 2,120 *8,460 



twenty hours. / 2,240 44.980 



Second specimen after \ 23.760 7,320 13,060 



twenty-four hours. / 24,000 7,500 14.000 



Third specimen after \ 11,740 25,940 



two days. / 11,140 27.520 



Fourth specimen after \ 1,720 1,920 



three days. / 2,040 1,200 



Fifth specimen after \ 2,280 9,580 



four days. / 3,840 10,549 



Three other specimens were examined after seven months, no 

 bacteria were found on the surface in any of the flasks, but after 

 shaking, 540 to 760 organisms per c.c. were counted. Hueppe 

 examined a service supply which contained only 16 bacteria when 

 drawn from the pipes. After allowing the water to stand for 

 two months, 11,280 bacteria per c.c. were found at the surface 

 and 123,750 bacteria per c.c. at the bottom. In these researches 

 the observers worked with a mixture of organisms, but there is 

 no doubt that different species behave differently as regards 

 sedimentation. 



