zi8 THE POPULAR SCIENCE MONTHLY. 



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 chem- 

 istry. 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 be- 

 coming 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 appropri- 

 ate ? 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 an- 

 swered 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 ah-." 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 possi- 

 bility 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 contami- 

 nated. 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 har- 

 monize, 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 be- 

 tween 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 indi- 

 cates the possibility of determining their quantity, though such deter- 

 minations are, at present, far from possible. Air was passed through 



