1885. ] Scientific News. 631 
the section being thrown under the knife blade, may, however, be 
obviated either by carefully trimming the vertical face in case it is 
accidentally painted (to allow for which the Aither margin of the 
paraffine may be left broader than the other three), or by drawing 
the knife s/ow/y, so that the first indication of a failure to cut 
through the vertical film may be recognized and the section held 
in place on the blade by a slight pressure with a soft brush, where- 
upon the knife will cut through the film and leave the section free. 
If by chance the paraffine block has been painted with too 
much collodion or with collodion which is too concentrated, thus 
leaving a shiny surface, the film should be at once broken by 
pressing it gently two or three times in quick succession with 
the end of a rather stiff, blunt, dry brush. This enables the col- 
lodion to dry quickly and thus prevents the softening of the 
paraffine. 
If the sections have a tendency to curl they may be flattened 
out on the slide by means of a brush, for a section thus impreg- 
nated with collodion may be handled during the first few seconds 
after contact with the Schallibaum mixture with much greater 
impunity than one not so treated. If the collodion has been too 
much thinned with ether, the fact will become apparent from the 
softening of the paraffine, and may be remedied by waiting for 
the evaporation of the ether, or by adding thicker collodion. 
This process can be in no way considered as a substitute 
for the ordinary method of cutting objects since it requires more 
time and closer attention to details, but for those cases where ` 
there is a liability to crumbling, or where sections of sufficient 
thinness cannot be procured free from folds, it will doubtless be 
found very serviceable-—Z. Z. Mark, Mus. Comp. Zoil, Cam- 
bridge, Fan., 1885. 
0 
SCIENTIFIC NEWS. 
— Ata late meeting of the Liverpool Microscopical Society, 
Mr. A. Norman Tate read a paper, which is reported in the 
English Mechanic, on the microscopical examination of potable 
dietetic purposes, he proceeded to speak of the importance of 
microscopical investigation in relation to water-supply, pointing 
out that it afforded better opportunity of determining the character 
of organic impurities, and that it might frequently assist in ascer- 
taining the character of the mineral constituents. He consi 
the arbitrary standards of purity as regards organic constituents, 
set up by some water analysts as being unsafe to use, without 
knowing the exact nature of such matters. And in deciding this 
the microscope could help. He then proceeded to speak of in- 
f 
