then transferred to water, Bilharzia hæmatobia (?), and Distoma hepaticum (Liver fluke of sheep). The guinea worm, Filaria dracunculus, penetrates into the subcutaneous cellular tissue of the legs of bathers; whilst leeches may fix themselves in the pharynx and cause much hæmorrhage. Metallic poisoning may be caused by pollution of drinking water with refuse from trades, and drainage from metalliferous mines, or from absorption by water of the metals used in the construction of distributing pipes, tanks, and cisterns. The amounts of mercury, copper, zinc, or arsenic, which must be present in the water to give rise to symptoms of poisoning, have not been ascertained; as regards lead, as little as grain per gallon may produce plumbism in predisposed persons. In the case of the poisoning of Louis Philippe's family at Claremont, grain of lead was found in each gallon of water. EXAMINATION OF WATER FOR SANITARY PURPOSES. It will be sufficient here briefly to sketch out a short scheme for the examination of water for medical and sanitary purposes. For further information on this subject reference must be made to the larger textbooks. The points to which attention should be especially directed are:-1. Physical examination of the water; 2. Microscopical examination of suspended matters and sediment; 3. Quantitative examination of dissolved solids; 4. Biological examination of the water. Physical Examination. 1. Colour. The water should be examined in a twofoot tube. Pure waters have a bluey-grey tint. A green colour indicates contamination with vegetable matter. Light brown, or yellow, is often due to the presence of sewage matters, but may be caused by peat or by salts of iron in the water. 2. Clearness or turbidity.-The purest waters are clear, bright, and sparkling. Polluted shallow well-waters sometimes exhibit these very qualities. 3. Taste. Polluted waters often have a disagreeable taste; but as often not, if the solids are perfectly dissolved, and the water is well aerated. Non-aerated waters have a flat taste. Iron in very small quantities can be tasted, but other salts in water cannot be tasted unless they are present in large proportions. 4. Smell.-The water should be put in a flask and gently warmed. Sulphuretted hydrogen, and the gases indicative of fermentation or putrefaction may thus be recognised. A suspected water may be put in a stoppered flask and kept in a warm place for a few days, to observe any changes that may arise, such as turbidity from commencing putrefaction. The physical characteristics of a water, though by no means conclusive in themselves, should not be neglected, as they give valuable corroborative evidence to the methods of examination presently to be described. Microscopical examination of the sediment.-The object of this examination, in a majority of cases, is to determine whether the water has been polluted with sewage or domestic refuse. Fibres of cotton, wool, or linen, starch cells, macerated paper, human hairs, yellow globular masses, and striped muscular fibre (undigested meat) with squamous epithelium cells are all indicative of contamination of the water with human refuse, and most probably with sewage. Amongst these matters, and feeding on them, will probably be found living organisms of a low type, such as bacteria (micrococci, bacilli, and vibriones), amœbæ, and infusoria. These organisms are not in themselves dangerous, but they indicate the presence of matters-chiefly organic-upon which they feed, and amongst them may be those disease-producing organisms which so often find their way into sewage (figs. 4-8). Pollution of water with vegetable matters may be recognised by the presence of vegetable cellular tissue, fungi and moulds, algæ, diatoms, desmids and confervæ (figs. 9-12). Amongst decaying vegetable matter will be found an abundance of microscopic living organisms, including bacteria, amœbæ, euglenæ, infusoria (vorticellæ, paramæcia, coleps, stentor, oxytricha, &c.), anguillulæ or water worms, rotifera or wheel animalcules, entomostraca (daphnia pulex (water flea) and cyclops quadricornis), amphipoda, isopoda, and tardigrada (water bears), the larvae of the water gnat, and the pupa forms of other insects, besides many others. It may be stated that the lowest organisms like bacteria, when present in large numbers, indicate that putrefactive changes are taking place, and generally that the presence of bacteria, amœbæ, and infusoria, must be regarded with great suspicion, because the polluting materials with which they are associated are more likely to be dangerous than the vegetable masses from ditches and ponds, amongst which the higher organisms are usually found. The sewage-fungus (Beggiatoa Alba) is found in |