56 



THE AMERICAN MONTHLY 



[March 



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 oft' 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 v/atch-glass suspended in a tall glass of compara- 

 tively small diameter, for instance a 500 c.c. measure glass. His 

 metliod of procedure was essentially to ftll such a measure glass with 



D IN PLACE. 



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 tmie 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. 



