what he is on a warm and murky day. The quantity of ozone in the air also varies. Perhaps our moods, our "spirits," are dependent upon ozone. Give us ozone enough, and the world will be happier and healthier. These are some of the ideas which have been advanced. Possibly there is some connection between these two very unlike things. Certainly much more accurate experiments than any which have thus far been made, are called for to prove the connection.
In the light of many experiments it appears exceedingly probable that one of the most important constituents of the air is aqueous vapor, and that variations in its quantity beyond certain limits are productive of serious results. The influence of carbonic acid, carbonic oxide, or ozone, upon the value of air is almost nothing as compared with the influence exerted by the moisture. This is a point that does not ordinarily receive the amount of attention which it deserves. A reliable hygrometer should be as frequently used in a dwelling as a reliable thermometer. It is undoubtedly a very difficult thing to regulate the amount of moisture in the atmosphere of dwellings, but more could be done than is done. The methods now adopted for this purpose are mostly exceedingly imperfect. Further, the importance of doing everything to regulate the amount is not sufficiently recognized, at least by the people at large.
As regards the water we drink, every one knows that cases are very common in which it becomes polluted in one way or another, and that disease results from its use. Innumerable chemical examinations of drinking-water have been made, and large numbers of methods proposed for the analysis. Some of the methods have been shown to be utterly unreliable; others to be questionable; very few indeed to give results which can be regarded as at all valuable. It is about as difficult at the present day to say what pure water is as it is to say what pure air is. Papers upon papers are written on the subject of water analysis. Some of these are based upon experiments performed; some are simply critical. Out of the mass of literature we gather some truths. One that stands out prominently is this, that the presence of chlorine, of organic matters, of ammonia, and of so-called "albuminoid ammonia," indicates that the water containing them is very probably contaminated through sewage, cesspool, privy, or barnyard refuse. By the later methods of analysis, the estimations of the quantities of the substances mentioned have become comparatively simple processes, so that now it is undoubtedly possible to pass a fairly reliable judgment upon the value of a given specimen of water. It is, however, still quite impossible to determine by chemical methods whether the typhoid-poison is present in water or not, just as it is still impossible to determine whether in the air there is present that indefinite something known as "malaria." There is still a great deal to be done in order that a close connection between disease and the condition of drinking water may be established. The open questions are to a con-
