The microscopical examination of water consists of the enumeration of the kinds of microscopic organisms (Plankton), and an estimation of their quantity.

It may serve any one or more of the following purposes:

(1)

To explain the presence of objectionable odors and tastes.

(2)

To indicate the progress of the self purification of streams.

(3)

To indicate the presence of sewage contamination.

(4)

To explain the chemical analysis.

(5)

To identify the source of a water.

(6)

To aid in the study of the food of fish, shellfish, and other aquatic organisms.

The term “Microscopic Organisms” shall include all organisms microscopic or barely visible to the naked eye, with the exception of the bacteria. It includes the diatomaceae, chlorophyceae, cyanophyceae, fungi, protozoa, rotifera, crustacea, bryophyta, and spongidae found in water.

Fragments of organic matter, silt, mineral matter, zoÖglea, etc., shall be considered as amorphous matter. The recording of amorphous matter usually serves no useful purpose and shall not be considered a part of the standard method.

Apparatus.—1. A cylindrical funnel about two inches in diameter at the top, with a straight side for nine inches, narrowed over a distance of three inches to a bore of one-half inch in diameter, and terminating in a straight portion of this diameter two and one-half inches in length. The capacity of this funnel is 500 cc. It shall be provided at the bottom with a tightly fitting rubber stopper with a single perforation and a disk of silk bolting cloth over the hole about three eighths of an inch in diameter.

2. A counting cell consisting of a brass rim closely cemented to a plate of optical glass. The shape and size of this cell are not essential but its depth shall be one millimeter. A convenient capacity is about one cubic centimeter.

3. An ocular micrometer ruled as follows: The ocular micrometer is commonly of such a size that with a 16 mm. objective and a suitable tube length, the largest square cuts off one square millimeter on the stage.

Procedure.—Filter 250 cc. of the water (more or less according to the clearness of the sample) through a one-half inch layer of quartz sand (washed and screened between 60 and 120 mesh sieves) supported by the disk of bolting cloth and rubber stopper at the bottom of the funnel. Suction may be applied to hasten the filtration.

Remove the stopper and catch the plug of sand and its entrained organisms in a small beaker or test tube, washing down the inside of the funnel into the beaker with 5 cc. of clean (preferably distilled) water. Agitate the mixture of sand, water, and organisms to detach the latter from the sand grains, and quickly decant the water and the organisms in suspension to a test tube. If desired the sand may then be again washed with 5 cc. water and the wash water added to the first portion.

Cover the cell partially with a cover glass, and by means of a pipette run the concentrate under the cover glass until the cell is completely filled.

Cover and place on the microscope stage in a horizontal position for examination.

Count the organisms in twenty fields, i. e., twenty cubic millimeters, estimating their areas in terms of Standard Units.

The Standard Unit is the smallest square in the ocular micrometer, and represents an area 20µ × 20µ, or 400 square microns on the stage.

Results shall be expressed in the number of Standard Units of each kind of micro-organism per cc. and also the total number of standard units of all kinds per cc. The general directions as to significant figures given under Turbidity shall apply also to the microscopical examination.

Caution.—Many micro-organisms, especially some of those causing odors, are so fragile that they are broken up in filtration, especially if the agitation of the filtrate is too vigorous. A direct examination of a fresh sample is therefore a useful supplementary procedure. For the same reason the concentrate should not stand long before examination. Also some organisms are carried by specific gravity to the top of the cell which should be scrutinized as well as the bottom layer each time.

It is always better to examine the micro-organisms in the field when possible, and for this purpose the sling filter has been devised consisting of a metal funnel slung to a pivoted handle, with a disk of wire gauze in the detachable lower end to support the sand. Filtration is hastened by imparting a whirling motion to the whole and utilizing the centrifugal force thus generated.

MICROSCOPICAL BIBLIOGRAPHY.

a.

Kean, A. L. A new method for the microscopical examination of water: Science, Vol. 13, p. 132, 1889; Eng. News, pp. 21, 276, 1889.

b.

Sedgwick, W. T. Recent progress in biological water analysis: J. N. E. Water Works Assoc., Vol. 4, pp. 50–64, 1889.

c.

——. A report of the biological work of the Lawrence Experiment Station: Examinations by the State Board of Health of water supplies of Mass., 1887–90, pt. 2, Purification of sewage and water, pp. 793–862, 1890.

d.

Parker, G. H. Report upon the organisms, excepting the bacteria found in the waters of the State: Examinations by the State Board of Health of water supplies of Mass., 1887–90, pt. 1, Examination of water supplies, pp. 579–620, 1890.

e.

Rafter, G. W. The microscopical examination of potable water, D. Van Nostrand Co., New York, 1910. (Contains bibliography.)

f.

Calkins, G. N. The microscopical examination of water: Report Mass. State Board of Health, pp. 397–421, 1892.

g.

Jackson, D. D. On an improvement in the Sedgwick-Rafter method for the microscopical examination of drinking water: Tech. Quart., Vol. 9, pp. 271–4, 1896.

h.

Whipple, G. C. Experience with the Sedgwick-Rafter method at the Biological Laboratory of the Boston Water Works: Tech. Quart., Vol. 9, pp. 275–9, 1896.

i.

——. Microscopy of drinking water, 3d ed., John Wiley & Sons, New York, 1914. (Contains bibliography.)