innocuous in themselves, yet afford evidence that the water is in such a position as to be liable to accidental contamination. 2. Living Forms. The lower forms of vegetable and animal life spring from a common point, so that it is in certain cases impossible to definitely ascribe life-forms to either kingdom; nevertheless, it is convenient to divide provisionally the microscopic life-forms into (a.) vegetable, (b.) animal. (a.) Vegetable.-The most common vegetable forms are confervæ, oscillatoria, volvocinæ, desmids, diatoms, and bacteria. To these may be added the green, or sometimes red, cells of palmellæ, and the moving reproductive spores of confervoids, charæ, &c. All of these, except the bacteria, diatoms, and certain spores, are distinguished by possessing cells holding "chlorophyll," and as such, always denote water which is exposed to daylight. Desmids, beautiful microscopic algae, consisting always of two symmetrical cells, are in colour remarkably green; one of the most common is a species of closterium (fig. 50). Desmids have been referred to by Dr. Macdonald as rather indicating a good water. It is true that desmids occurring by themselves, with no other indication of animal and vegetable life, could in no way be pronounced injurious. The fact, however, remains that, as a result of over ten years' experience in the almost daily analysis of Fig. 50. water, the writer has never found desmids except in more or less surface supplies of water abounding with impurity. The diatoms, which are composed of a siliceous skeleton clothed by a sarcode substance, consist, like the desmids, of two exactly similar parts; they possess no chlorophyll, and probably belong to the animal kingdom. Fig. 51 is Diatom vulgare, very frequently found, and by itself certainly affording no indication of a bad water. fact, diatoms generally are of little importance. Fig. 51. In Bacteria. This family of late years has excited a most extraordinary amount of attention and investigation, from the fact that certain forms of bacteria have been found the invariable associates of some virulent diseases, as, for example, malignant pustule. Bacteria are forms of extreme minuteness, the earliest appearance being that of points just visible with the highest powers of the microscope. Cohn defines them as chlorophyll-less cells of globular, oblong, or cylindrical form, multiplying exclusively through cell division, and vegetating either isolated or in families. Bacteria occur in water, (1.) as clouds, well seen if a dead animal is allowed to putrefy in a salt water aquarium; (2.) as an iridescent film on the surface of water; (3.) as a pulverulent precipitate. The precipitate, where bacteria are plentiful, may form quite a layer, looking to the naked eye like fine white clay, but consisting of heaped up myriads of bacteria. Bacteria possess a motionless and an active condition; the movements are either those of rotation round their axis, or a passive bending and unbending of the curved forms. They are often in water very difficult to observe, because their index of refraction is so like that of water itself. The beautiful photographs which Dr. Koch has taken of various bacteria* show that they are not bounded by very definite lines, but that the dark body gradually blends into a gelatinous border or membrane. However difficult it is to observe bacteria when unstained, the aniline colours easily make them visible, and then it is at once seen how widely disseminated they are. Dr. Kocht recommends for photographic purposes a fluid containing bacteria to be treated thus: A drop of the fluid is taken out and placed on a glass slide, and covered with the usual thin covering glass. When the drop is dry or nearly so, it is remoistened with a solution of acetate of potash, 1:3, and then, if required, stained by an aniline brown; for mere detection of bacteria the methyl violet before alluded to is best, and one or two minutes immersion in a watery solution is sufficient. Cohnt divides bacteria thus— I. SPHÆROBACTERIA (Kugelbacterien), minute jostling spheres. The cells are of an oval form, the dark body passes into the continuous membrane, and is not to be well separated from it ; they occur in short chains or groups of 3, 4, and 8.§ To this division belong the ferment-producing (zymogenous) bacteria, as, for example, Micrococcus urea, always found wherever there is ammoniacal putrefaction. Another group is the Chromogenous, or colour-producing, as the M. prodigiosus, or blood-stain on bread, M. violaceous, discovered on slices of boiled potatoes, and many others. Another important subdivision is the "Pathogenous," or disease-producing, e.g., M. diphtherici,|| M. vaccinniæ, &c. II. MICROBACTERIA (Stäbchenbacterien.)—Minute short rods. "Untersuchungen über Bacterien; Verfahren zur Untersuchung, zum Conserviren u. Photographiren der Bacterien, von Dr. Koch. Beiträge zur Biologie der Pflanzen." Breslau, 1877. + Op cit. "Untersuchungen über Bacterien, von Dr. Ferdinand Cohn. Beiträge zur Biologie der Pflanzen." Breslau, 1872. § Pasteur calls single bacteria "monads," when in gelatinous masses "mycoderma." [Cohn's "Zooglea."] || Oertel: Experimentelle Untersuchungen über Diphtherie. Deutsche Archiv für Klinische Medizin. Band vii., 1871. This second class is separated from the first by their physiological activity, by their short cylindrical form, and the spontaneous movement of the cell. B. termo is par excellence the bacteria of putrefaction, and is the little organism to be found whenever and wherever any animal substance decays. The bacteria nearly always occur in pairs or dividing; they consist of very minute, little, short, cylindrical masses, either clear and transparent or blackish; there is a rather thick surrounding membrane. B. lineola, another member of this family, is larger, and is found in brooks and standing water; the cells are four times longer than broad, and have a strong refracting fatty nucleus. III. DESMOBACTERIA (Fadenbacterien).—Thread or filament-like bacteria. The bacteria are in the shape of threads, some of them of great length. B. anthracis Cohn puts in this class. IV. SPIROBACTERIA (Schraubenbacterien).-Spiral or screw-like filaments. This class includes vibrios and various species of spirillum. The universal presence of bacteria, especially of the more common kinds, must render the microscopist cautious about conclusions, if he finds a member or so in water. If, however, water contains them in sufficient quantity to be a marked or unusual feature, such a water should be emphatically condemned. (b.) Animal Forms.-Without taking into consideration various water insects which can be seen with the naked eye (e.g., water fleas), but confining the attention solely to the microscopic forms of life, there is such an inexhaustible variety of the latter that it takes a special study to ascribe to each form its particular species; fortunately, this to the analyst is not necessary, and it may at once be laid down that if the deposit from a reasonable quantity of water (for example, a gallon) exhibits forms of infusorial life, the water cannot be pure. For although from all natural water, if a sufficient bulk be taken, it is possible to extract life-forms, yet all good drinking-water is devoid of such when moderate quantities are taken for the search. There are, however, certain animalcules (types of which are figured) that specially point to sewage contamination. This class have been called "saphrophiles." They include most ciliated forms, such as paramecium, (fig. 52,6), glaucoma, as well as vorticella (fig. 52,1), amoeba (fig. 52,8), and others. It will not be necessary to use any special colouringagents to see infusoria, for they are quite sufficiently visible without any special reagent. M. A. Certes has, however, found out a colouring-matter which concentrates itself in certain parts of living infusoria, and may, therefore, be of some utility; this *Under the saphrophiles belong all vegetable fungi, e.g., leptothryx and infusoria thriving in filth. WATER. 545 reagent is quinoleine or cyanine, and it appears chiefly to colour the fatty parts of the protoplasm. He considers it a reagent for living fat.* Fig 52. (6.) (2.) (8.) (9.) 1. Colony of Vorticella. Glaucoma scintillans. 5. Glaucoma Gibba. 6. Paramecium aurelia. 2. Oxytricha lingua. 3. Pellionella. *Comptes Rendus, xcii. 425. 26 4. 7. B. Cultivation of Germs, Fungi, &c.-If a bottle of water carefully corked, and placed at a fermentation-temperature 20° to 24°, contain any putrescent matter, the water acquires a disagreeable smell, and when examined microscopically swarms with B. termo or other forms of low life. This simple test anyone can make for himself, and it is perhaps too much neglected. The best way to examine water thus fermented is to place a quantity of it in the special tube figured at p. 540; and, after adding a few drops of a 1 per cent. solution of osmic acid, to allow it to stand for some hours, then collect the sediment in the cap for microscopical examination, after the addition of methyl violet and other staining reagents. The osmic acid kills the life-forms, and they gradually sink to the bottom. Heisch's Sugar Test.-Another fermentation method now much in use among analysts, is simply the addition of sugar to the water under examination, when, if the water contains the merest trace of sewage, a special fungus develops. The details of the test are as follows: A clean stoppered bottle, of any convenient size, is filled with the water, and a few grains of pure white sugar added. The bottle is now to be carefully stoppered, and placed at a fermentation temperature (26° to 27°). The growth of the fungus is rapid; at first small cells with a bright nucleus appear, changing within six hours to moniliform threads, and finally to cells mixed with mycelium. To trace the stages of the growth, it will be necessary to examine from time to time the liquid by the microscope; but the coarser changes may be watched with the naked eye: any water decidedly contaminated by sewage becomes quite turbid with the fungus in about twelve hours. C. Experiments on Animals and Human Beings.—The biological examination of water embraces actual experiment on animals. Concentrated alcoholic, ethereal, or aqueous extracts of the water residue are injected by a fine syringe subcutaneously into small animals. From this important and direct method much may be hoped. A few experiments of the kind have been performed on the Continent; but in England, although foxes may be dug out to be eaten alive by hounds, and ratcatchers may poison rats by the gross, scientific men are unable, save under practically prohibitory restrictions, to advance biological science by the only satisfactory way, the use as a reagent for obscure poisons of life itself. Experiments upon human beings are made necessarily daily, and on enormous masses of population. It is a kind of evidence that is most easily obtained, and nothing is more clearly proved than the fact, that a large population may drink a sewage-polluted |