(107) Examination and Analysis of Water.1

It need scarcely be remarked that it is not the water per se the analyst analyzes, but his researches are directed with the object of discovering what substances are held in solution or suspension in the water.

The medical officer of health need not be a professed analyst, but he certainly should be able to make a qualitative and quantitative analysis of such a nature as to determine the main constituents, and should also be able to interpret an analysis. The examination falls under the following heads:

I. Examination by the Senses.-Smell, taste, and general appearance.

II. Biological.-Embracing microscopical appearances; cultivation of fungi and dormant germs; experiments on animals; experiments on fish.

III. Chemical methods.

(108) I.-Examination by the Senses.

Water that is evidently turbid, that possesses an odour and unpleasant taste, requires no analytical process to condemn it; such a water is unsuitable for drinking purposes. A water possessing even any one of the above bad qualities will, as a rule, on further examination be found considerably polluted.

Colour. -A 2-foot tube, the ends closed with plate glass is generally used for ascertaining the colour of water. It is only the purest water that examined in this way possesses a faint, blue tint. The great majority of drinking waters are more or less coloured with various hues of brown and green. Dr. Tidy uses for the purpose of giving a definite statement of " colour" two hollow wedges, the one filled with a blue solution, the other with a brown solution, by sliding the one wedge over the other any combination of brown and blue may be produced: the colour of the water in the 2-foot tube is thus "matched" by the wedges, and the conjoint colour expressed as the combination of so many milli

1 In the author's work on Foods, their Composition and Analysis, Lond., 1888, will be found in great detail processes for water analysis.

metres of the colours. It is found that a very close relationship between the amount of organic matter in the water and the depth of brown colour exists.

Smell. This is best ascertained in the following manner :-Half a litre or a litre of the water is warmed to blood heat in a flask, the flask being closed with a cork or stopper, a long glass tube three-quarters of an inch in diameter is introduced, and the water sucked up once or twice so as to wet the sides of the tube thoroughly; still keeping the tube in the flask but so that its lower end is out of the water, one nostril is applied to the upper end and a prolonged inspiratory sniff is taken. In this simple way, very faint odours may be appreciated.

(109) II.-Microscopical and Biological Methods.

To make a microscopical examination of water it is necessary to examine the sediment which falls in scanty or copious amount according to the quality of the water. To do this, the author's tube will be found very convenient.

Its capacity is about a litre. It is in principle a big pipette, so arranged that all the sediment collects in a small glass cell or cap. The little glass cell, c (Fig. 27), is adjusted so as to close the end of the tube, and then FR the water is poured in and allowed to subside. At the end, say of twenty-four hours, the rod, R, is inserted so as to stopper the pipette-tube from the inside, now the cap c with its cubic centimetre of water may be removed without interfering with the main bulk. From this small concentrated bulk, drops are placed under the microscope without any preparation, others are divided up on several slides and treated with (1) dilute iodine solution, (2) drops are dried and examined for bacteria by staining with methyl violet, and (3) other drops are coloured with carmine and glycerin which has the FIG. 27. property of staining the nuclei of cells red.

C

A litre of water which throws down only a little sand and unrecognisable débris destitute of living forms may be considered, in a microscopical sense, pure.

The matters found in a water are—

1. LIFELESS FORMS.

(1). Mineral matters, e. g., sand, clay.

(2). Vegetable matters.—In all shallow waters, in rivers, and in all water which is exposed to the atmosphere, the microscopist seldom fails to find vegetable débris in the shape of dotted ducts, spiral vessels, parenchymatous cells, bits of cuticle with the hair still adhering, the down of seeds, and other similar matters.

(3). Dead animal matters.—(a) Purely animal, such as hairs from domestic or wild animals, striped muscular tissue, scales of moths or other lepidoptera.

(b) Human débris-human hair, epithelium.

(c) Manufactured matters-wool, silk, and other matters.

2. LIVING FORMS.

(a) Vegetable. The most common vegetable forms are confervæ, oscillatoria, volvocina, desmids, diatoms, and bacteria. All of these, with the exception of diatoms and bacteria, contain chlorophyll, and are therefore of a green colour. Water containing these green organisms must of necessity have been exposed to air and light.

(b) Animal Forms.—Neglecting various water insects and living forms which can be seen by the naked eye, such as water fleas, the most frequent moving organisms seen in water are various forms of infusoria. These are for the most part propelled by the aid of fine motile hairs called "ciliæ."

Bacteria. These are best discovered in a water by the method of cultivation.

The method of cultivation which the writer has found simplest is as follows:

The first step is to obtain a perfectly sterile gelatinous media. This is done as follows-a pound of any lean meat is chopped up as finely as possible, and allowed to soak in about 700 c.c. of cold water for twelve hours. At the end of that time the red, feeblyacid liquid is separated in part by decantation, and in part by filtering through a linen cloth. 100 grms. of commercial gelatin are soaked for several hours in about 300 c.c. of water, and ultimately dissolved by the aid of heat: the gelatin solution is added to

the meat infusion in a flask, a fractional portion taken and its acidity carefully determined by decinormal soda. Sufficient sodic carbonate is now added to neutralize the whole liquid, as well as about a grm. of common salt and a grm. of glucose. The flask with its contents is now heated by immersing it in boiling water for two or three hours. The albuminous portion coagulates, and the coagulum carries various insoluble matters with it. The liquid is now filtered (the filter being kept hot by a steam jacket) into several Lister flasks; the flasks are well plugged with sterile cotton wool, and then submitted for three successive days to the heat of the water bath for a couple of hours. The result is a sterile jelly solid at ordinary temperatures.

The cultivation takes place on glass plates 4 inches × 4 inches; on to these plates are cemented glass rings inch broad, inch deep, and 38 inches in diameter, thus forming large shallow cells. The rings are cemented on to the plates by means of the jelly itself as follows:-The rings and plates are both heated to a high temperature in a hot air oven; while still hot a few drops of the liquified jelly are dropped from the flask on to the ground surface of the

ring. The ring is then applied to the plate, rotated and put face downwards under a dust-proof shade to cool and set. The water to be examined is weighed in a simple form of drop-bottle (see Fig. 28), a drop or two is placed by means of the pipette stopper on to the plate, and the bottle reweighed so as to obtain by difference the weight of the drops. The nutrient gelatin melted at a gentle heat in the flasks is now poured into the cell so as to form a layer th of an inch deep. The glass cell is then put into a special chamber formed of two shallow glass dishes, the one inverted over the other; the air of the chamber is kept moist by saturating a piece of blotting paper at the bottom with a solution of mercuric chloride (1:100). After from three to five days, little dots or colonies appear in the gelatin; these are centres of development, each centre being a colony containing many thousands of individual forms. They may easily be divided by examining them under a low power into bacilli, micrococci and fungi, they may also be divided into liquifying and non-liquifying according as to whether the gelatin is liquified by their action or not.

FIG. 28.

The

glass plate is conveniently ruled by a diamond into squares.1 Provided the colonies are not very numerous, they are easily enumerated, but such liquids as sewage require to be largely diluted with sterile water before taking droplets for examination.

A good water seldom contains more than 1,000 colonies per gramme when cultivated within 24 hours after collection. If a long time elapse between the collection of a water and the cultivation, a cultivation gives but little information, for no water is absolutely sterile, and the power for increase in micro-organisms is prodigious. It is probable that a number of different kinds of micro-organisms is more important as indicative of pollution than a large number of one kind. Hitherto the method of cultivation has not been of the high value which it was first confidently anticipated it would be, for the methods employed develop common micro-organisms grown at a low temperature, and pathogenic organisms require a comparatively high temperature such as 20° to 30° Cent., the liquifying organisms in practice almost invariably prevent cultivation longer than a few days, the whole mass of gelatin becoming liquid and running together; and lastly the investigation requires much time. It is to be hoped that future research may yet make the method practically useful; there are several researches which point out to a possibility of isolating the pathogenic from the non-pathogenic; for instance, Chantemesse and Widal have shown that trichloride of iodine in the proportion of 1 to 500 in nutrient gelatin inhibits the growth of all common micro-organisms, but the so-called typhoid bacillus will, nevertheless, grow, and by these means they were able to isolate it from other micro-organisms in excreta."

(110) Qualitative Examination of Water.

The qualitative chemical examination of a water may be restricted to the addition of a little "Nessler's" solution, when, if ammonia is present, there will be a greater or less yellow, amber, or brown colour-the detection of nitrites, nitrates-the reaction. of the water and the presence or absence of metals.

Nitrites.-The best tests for nitrites are (1) the metaphenylenediamine test; (2) Meldola's test; (3) the napthylamine test.

1 There are now glass plates sold divided into squares for the purpose of counting bacteria.

2 In the chapter treating of enteric fever will be found further details as to the possibility of isolating the bacillus of typhoid fever.

M