846 THE AMERICAN MONTHLY [Nov 



consists in the use of a cylindrical glass funnel (fig. 1) 

 similar to the one designed by Mr. D. D. Jackson for the 

 Massachusetts State Board of Health, but different from 

 it in having a capacity of 250 instead of 500 c. c. and in 

 having graduations marked upon the sides. This funnel 

 may be conveniently carried and its graduation renders 

 the use of a second measuring glass unnecessary. When 

 in use it may be supported on a wire frame, which any 

 ingenious person can make. In place of the test-tube it 

 has been found convenient to use tube vials (fig. 2) having 

 square ends. These require no racks and are not easily 

 tipped over. The pipette for washing the sand might be 

 dispensed with if one of the tube vials was graduated, 

 but as much depends upon accuracy in concentrating 

 the sample it is best to use a short pipette (fig. 7). The 

 sand (fig. 3) used in the filter should be perfectly clean 

 and of such size that its grains will pass through a sieve 

 having 60 meshes to the inch, but not through one having 

 100 meshes. Crushed quartz makes the best filtering 

 material and should be used when obtainable. The discs 

 of bolting cloth (fig. 6) mav be easily cut out with a wad 

 cutter. The filtered water may be used for concentrating 

 the organisms, or it is possible to employ preservative 

 fluids in case the microscopical examination must be 

 deferred or it is desired to keep the specimens. The cell 

 (fig. 8) for holding the concentrated fluid may be made 

 by cementing a brass rim to an ordinary glass slip. It 

 should be 50 mm. long, 20 wide and 1 mm. deep, thus 

 lioldiug just 1 c. c. and having a superficial area of 1,000 

 !^q. mm. 



A very simple microscope will answer for this work. 

 A large stand is too valuable and too heavy for the rough 

 usage in ihe field, and a cheap, light stand with a l^inch 

 or I inch objective and a Nu. 3 ocular will answer equally 

 well. The ocular must be providi^d with a micrometer, 

 .so that the observer may count the nuinber of organisms 



