mitted us to take a survey of the field, we should find that the proof could be made conclusive.
But the discovery of new substances to be used as remedies does not furnish the only bond of connection between medicine and chemistry. Nor is it by any means the most important one. For, as the tendency of the present generation of physicians is, I think, to rely less and less upon the action of drugs and chemicals, and to pay more and more attention to the circumstances surrounding the patient, so the discovery of purely remedial agents is becoming day by day of less importance, and the accurate study of those substances which we all necessarily make use of—air, water, food in its various forms—is becoming the great problem in medicine. Thank Heaven! the day of the old woman who knows what is "good for" everything is waning. She exists still in a thousand forms, sometimes in skirts and sometimes in trousers, but the natural growth of modern ideas will eradicate her, though the process will take generations for its completion.
What is pure air? What is pure water? What food is appropriate? These are questions which can only be answered by him who is versed in chemistry. The very fact that discussions are still going on in regard to these subjects indicates clearly that they can not be answered easily, and yet no one doubts their fundamental importance.
For years men were satisfied with the belief that an increase in the amount of carbonic acid, beyond a certain point, was the cause of the evil effects experienced in breathing "foul air." The old familiar stories that have been told to prove the injurious character of the gas are still told in lectures on chemistry, and text-books of chemistry, and in medical books without number. Still, as most of you probably know, it has long since been proved by direct experiment, beyond the possibility of a doubt, that the amount of this gas may be increased to one twentieth of the volume of the air without producing any serious or even disagreeable effects upon those who breathe the air thus contaminated. This is true, however, only when the carbonic acid is mixed with the air as a pure substance. If introduced in the ordinary way, by the breathing process, different results are obtained, and it is found that, under these circumstances, the quantity of carbonic acid can not exceed one part in 1,000 of air without serious effects upon those who breathe the air. The two results, apparently, do not harmonize, but, when we recognize the presence of other substances, of organic matters, in the air, which are given off from the body together with the carbonic acid, and in quantities proportional to the quantities of the latter, we can readily see that there may be some connection between the amount of the carbonic acid present and the fitness of the air for breathing purposes. Such organic matters can easily be detected in the air, and they have recently been found by a method which indicates the possibility of determining their quantity, though such determinations are, at present, far from possible. Air was passed through
