86 
bers of microscopical examinations are now 
being made [during the past eight years 
more than 40,000 have been made in Mas- 
sachusetts alone], and the rapid growth of 
the new science of sanitary biology is de- 
veloping numbers of well-trained observers 
wide awake to the value of these problems 
and well able to undertake the work. What 
is needed is cooperation. 
Various methods have been employed 
from time to time for determining the char- 
acter and amount of microscopic life in 
water. Those interested in the subject 
from the piscatorial standpoint have usually 
employed some sort of net for straining the 
organisms from the water and concentrating 
them for the microscope. One of the best 
devices of this kind is that devised by 
Professor Reighard and used with good 
results for studying the plankton in Lake 
Michigan. It consists of a conical net of 
fine bolting cloth, at the small end of which 
there is a ‘bucket,’ made by covering a 
metal framework with some of the same 
bolting cloth. The apparatus is hauled 
through the water, filtering a column of 
water whose cross section is the same as 
the circular mouth of the net and whose 
length is equal to the distance through 
which the net is hauled. The organisms 
are caught by the fine bolting cloth and are 
ultimately washed into the bucket. The 
collected material is then removed by an 
ingenious arrangement, measured and sent 
to the laboratory for microscopical examina- 
tion. By this method one is enabled to get 
a good idea of the total amount of suspended 
matter in the water, but it can hardly be 
called an accurate method of obtaining the 
number of living organisms present, as the 
net Sweeps in amorphous matter as well as 
organisms and some of the smaller forms 
undoubtedly escape through the bolting 
cloth. Moreover, the amount of water 
actually filtered cannot be told with a great 
degree of accuracy. Nevertheless, the 
SCIENCE. 
[N.S. Vou. VI. No. 133: 
method is one of value, particularly for 
securing the larger and rarer forms of 
rotifers, crustacea, etc. 
Sanitarians who have studied the micro- 
scopical organisms in water supplies have 
usually employed very different methods 
from the above, partly because they have 
been interested more especially in the 
smaller forms, but chiefly because their 
operations have been confined to the small 
quantities of water sent to the laboratories 
for analysis. During the last decade the 
old methods of sediment examination have 
given way to the filtration methods. The 
Sedgwick-Rafter method, which is most 
used at the present time in laboratories of 
water analysis, is carried on as follows : 
A portion of the water to be examined is 
measured out in a graduate and filtered 
through a thin layer of quartz sand placed 
at the bottom of a glass funnel upon a 
perforated rubber stopper, the hole in which 
is capped with a dise of bolting cloth. 
When the water has filtered, the organisms 
will be found upon the sand, while the fil- 
tered water will be free from them. The 
rubber stopper is then removed and the 
sand washed into a test tube, with a meas- 
ured quantity of distilled water delivered 
from a pipette. Usually 250 or 500 c. ec. of 
the sample are filtered and the sand washed 
with 5 ¢.c. The test tube is then thor- 
oughly shaken and the water decanted into 
a second tube; the organisms being lighter 
than the sand, will pass off with the water, 
leaving the sand clean upon the walls of 
the first tube. In this way the organisms 
are concentrated 50 or 100 times. One ec. 
ce. of this concentrated fluid is then trans- 
ferred to a counting cell, which just holds 
it and which has a superficial area of 1,000 
sq.mm. After putting a thin glass cover- 
slip over this cell it is transferred to the 
stage of the microscope for examination. 
The eye-piece of the microscope is fitted 
with a micrometer in the shape of a ruled 
