1890. | RAFTER—BIOLOGICAL EXAMINATION OF WATER. oH 
The method of Prof. Sedgwick came to my notice about nine 
months ago, and after examination it appeared quite evident that 
considerable additional refinement was possible, and to this l addressed 
myself with the result of finally perfecting the technique in the manner 
which I now briefly lay before you. 
In the method, as I now use it, the sand is supported upon a plug 
of wire cloth placed at the lower end of the funnel stem, as shown in 
figure o. After placing the plug the sand is run into the funnel, lightly 
pressed to place with a glass rod, and from 20 to 4o c. c. of freshly 
filtered water allowed to run through in order to insure thorough settling 
of the sand before actually beginning the filtration. The amount of 
water to be filtered is gauged by the number of organisms which it 
" contains, as ascertained by preliminary inspection. Generally, however, 
as large a quantity should be used as can be conveniently filtered with- 
out clogging the sand so much as to render the completion of the 
process too prolonged, and for ordinary samples I have fixed upon 500 
c. c. as the proper amount. In the case of very pure waters a larger 
amount will be desirable, and for such 1ooo c. c. may be adopted as 
a convenient unit. 
Pion 
90 1777, 
2omm, 
Sechon 
fg) ams 
Fig.4. Plan and Sechon of 
Cell with cover glass, 
Experience indicates that however carefully the sand may be 
placed, the filtration at the beginning will not be as complete as further 
on, and in order to insure the certain removal of all the smaller 
organisms the first 100 to 150 c. c. of the filtrate is returned to the 
funnel and passed through the sand the second time. The funnel is 
allowed to stand until the completion of the filtration, when it is 
found on examination of the filtrate that nearly every organism has 
been removed and we have the result that the organisms originally 
