INTRODUCTION 11 



late war when applied in small doses in somewhat modi- 

 fied form. 



Colonel Auld's authoritative exposition of gas warfare 

 is not included to make the reader as enthusiastic about 

 this tool of civilized man as it has made a number of gen- 

 erals belonging to the five continents. The introduction 

 of "gas" in war has done as much to revolutionize war- 

 fare as the introduction of the aeroplane. For good or 

 for evil, gas warfare has come to stay, unless a miracle 

 happens and men begin to use their hearts as well as their 

 heads. 



We can at least point to one constructive achievement 

 indirectly due to the development of gas warfare. Sev- 

 eral types of gas masks have already been successfully 

 used by miners and others as protection against poisonous 

 fumes. 



The physicist needs his mathematics ; the chemist rests 

 more and more on physics ; and so it is no wonder that the 

 biologist and the medical man have turned to physics and 

 chemistry for further inspiration. Some of the most not- 

 able achievements in biology and medicine in recent years 

 have been due to the application of the two more funda- 

 mental sciences to them. The elucidation of the nature 

 of enzymes is a case in point ; Professor Loeb's and Pro- 

 fessor Henderson's articles are other and noteworthy ex- 

 amples. 



Still it is true to say that in medicine the most notable 

 achievement so far has been the development of the science 

 of bacteriology, the foundation of which we owe to the 

 chemist Pasteur. The story of this development is told 

 by Dr. Flexner. 



The chemist Pasteur inspired Lister the surgeon; and 

 Dr. Keen, who served in the Civil as well as in the late 

 war, tells the story of Before and After Lister. 



From the physical, through the biological, to the psy- 

 chological sciences is a very natural evolutionary process. 

 Experimental psychology, of which psycho-analysis may 



