self-purification takes place only if the water has not been previously sterilized by boiling, and protected afterward against the entrance of germs. But if a sterilized water has been subsequently exposed to the air or mixed with ordinary water, it undergoes the same changes as waters that have not been sterilized; its oxidizable power and its ammonia decrease, while nitrous or nitric acid is formed. If, therefore, the development of organisms in the water is rendered impossible, self-purification is also impossible. Direct oxidation by atmospheric oxygen certainly does not take place; and, if ozone and hydrogen peroxide play a part, it is a subordinate one. The kind of living beings which effect the purification of waters will differ greatly according to circumstances. Such a change of species has actually been observed in one and the same water-course in the different stages of its pollution. Self-purification may take place, even when industrial refuse is allowed to flow into the water in addition to organic pollution. Dr. J. Soyka has made experiments on the power of the soil to absorb poisonous substances and destroy them; and has showed it to exist in the cases of strychnine and a considerable number of the organic alkaloids. His experiments have not been extended to the ptomaines. Nevertheless, we must beware of supposing that the treatment of foul waters can safely be left to Nature. Where the supply of polluting matter is continuous in time and space, natural purifying agencies fail. An important lesson to be learned from the researches of Emich and Soyka is, that the microbes, both of earth and water, are not all to be regarded as disease-generators. On the contrary, certain kinds of them are converting malignant matter into forms in which it is harmless, or even useful. Hence, it is at least possible that, in the application of disinfectants or "germicides," there is room for discretion.
School Life and Health.—Dr. Thomas Whiteside Hine, of Bradford, England, has made inquiries into the effect of school life upon the mortality of children, taking as the basis of his conclusions the reports of deaths among children of from five to fifteen years old, persons of that range of ages being regarded as probably those upon whom the effects of school life and work would be most marked. Comparing the returns from 1871 to 1880 with those from 1861 to 1870, he finds that while the mortality of children from all causes and from zymotic diseases—on which school influences are negative—has considerably diminished, their mortality from nervous diseases—the direction in which school influences would be most felt—has exceptionally remained stationary. To this he adds that the figures for 1881 and 1882 likewise show identical results in both instances. Further than this, he finds that there has been an improvement in the death-rate from nervous affections among children below five years, who are out of school, or have been in it for only a short time. Yet the whole of the mischief must not be attributed to the effect of schooling alone; but, as all the world lives faster than it did, the nervous system of children is likewise stimulated at the present day to an extent unknown a generation ago, and greatly to their disadvantage. The existence of such sources of mischief in the habits of the day supplies a strong reason why all school influences calculated to enhance the mischief should be removed.
Seasoning Timber.—Of the common sense of the question of seasoning timber, Mr. Thomas Blashill says, in an address on the general subject: "Wood must not be dried so quickly that it will be made unsound by cracks. It must not be dried so much that it will absorb fresh moisture when it comes into the atmosphere in which it has permanently to remain. It is not merely a question of time, but of judgment, the objects being to see that the timber is gradually reduced in scantling as it dries, and so treated in temperature and stacking that it neither splits nor gets out of shape. ... To sum up the whole class of questions connected with seasoning, we want timber that will not shrink after it is brought into use, that will not work or twist out of shape, will not decay through damp, and will not be destroyed by insects. Wood may also be indurated, that being the result of polishing and of varnishing to some extent. Upon the whole, it is desirable to encourage all means of treating wood so that it may possess some
