Microscopical Examination of Water. By W. L. Scott. 239 
fluid by means of some neutral fatty composition, for which 
purpose I prefer a mixture which may conveniently be called “ Ozo- 
vaseline ” ; of 
35 parts. 
65 „ 
100 
of which a small sample is before you. With the aid of some zinc- 
plate or boxwood stencils, ozo-vaseline in the fluid state may be 
so applied to the filter-disks that they present the appearance of 
those herewith. 
Using filters of this description, it is evident that the whole of 
the suspended matter, living and dead, mineral and organic, present 
in a given quantity of water, say 7000 grains (or any convenient 
multiple thereof), can be, as it were, concentrated or condensed into 
X <ro th of its normal bulk, or even less if meded, without wasting 
the major portion of the water itself, and without injuring or altering 
the characters of the various organisms finally contained in the 
small and impervious cone forming the bottom of the filter. Larger 
or smaller quantities of water can, of course, be operated upon, as 
may be found expedient, provided always that the principle involved 
be rigidly adhered to, viz. that some definite measure be used 
throughout, by preference referable to the imperial gallon ; so to 
afford a means of comparing one sample of water with another, 
both as regards varieties and the number of the organisms present 
therein. 
The filter-paper ordinarily met with will, without doubt, afford 
a free passage to many of the smaller organisms present in many 
waters ; it becomes necessary, therefore, to adopt some means of 
stopping their egress. For this purpose I find a very thin struc- 
tureless collodion exceedingly useful ; filter-paper dipped herein, 
and allowed to dry, may thus be rendered of any required degree of 
porosity. In practice I find it convenient to keep ready two or 
three varieties of paper thus treated. 
It is obvious that by this fractional filtration process it is possible 
to collect together in a rapid manner, and in the compass of a few 
drops of liquid, all the organisms previously diffused throughout a 
large quantity of water without the doubtful labour of the ordinary 
“fishing” processes, and without the great loss of time attendant 
upon the “settling” and “decantation” plans generally recom- 
mended. 
Again, in the examination of adulterated milk, it frequently 
becomes a question of material importance whether pure or con- 
taminated water has been employed to dilute the natural secretion 
of the cow. By following the plan I have endeavoured in general 
s 2 
Vaseline 
Ozokerite 
