1890. | RAFTER—BIOLOGICAL EXAMINATION OF WATER. 35 
obtaining specimens was to fasten a bag of plain muslin to a kitchen 
faucet and allow the water to flow through until the pores of the cloth 
were partially clogged with the arrested organisms ; the bag was then 
removed from the faucet, turned wrong side out and the organisms 
washed off into a beaker or tumbler. Subsidence took place in a few 
minutes, after which specimens for examination were selected by 
dipping with a small tube or medicine dropper from different depths. 
This was the only method used during the two years that the Micro- 
scopical Section was engaged upon this special study, and indeed was 
as practical a method as any that had up to that time been devised. 
McDonald, in his Water Analysis, had suggested several years 
before the use of a watch glass suspended in a tall glass of compara- 
tively small diameter, for instance a 500 c. c. measure glass. His 
method of procedure was essentially to fill such a measure glass with 
the water to be examined, and to suspend in it at the bottom a watch 
glass, after which the whole, lightly covered, was set aside for perhaps 
24 hours. At the end of this time the water was siphoned off with a 
piece of India rubber tubing so as to leave only a thin stratum of liquid 
in the watch glass at the bottom. The watch glass was now raised and 
samples selected with a pipette for examination on a glass slide, or the 
watch glass itself placed upon the stage of the microscope for direct 
examination. This method was, at the best, crude and unsatisfactory, 
and as it could give only qualitative results, it is doubtful if with any 
operator it has ever passed much beyond the experimental stage. The 
method used by the Microscopical Section was somewhat more simple, 
and gave all the information that could be obtained by the use of the 
more elaborate method of McDonald. 
Mr. Hogg in the tenth edition of his work on the microscope has 
added a chapter on the microscopical examination of potable water, 
but without advancing any methods other than those _ previously 
announced by McDonald. Likewise Zvemann and Gértner, the recent 
German authorities, have added nothing to our knowledge of this part 
of the subject. 
The matter of qualitative examination of the micro-organisms in 
potable water remained in about the state indicated by the foregoing 
until a little less than a year ago, when Prof. Wm. T. Sedgwick, of the 
Massachusetts Institute of Technology. worked out a method for 
making the quantitative determination as well.* This consists, first, in 
the concentration of the organisms in a large amount of water into 
so little water that they may be readily examined under the con- 
ditions imposed by microscopical technique; and, second, of an 
*See paper on Recent Progress in Biological Water Analysis in Transactions of New England 
Water Works Association September, 1889. 
