THE 



POPULAR SCIENCE 

 MONTHLY. 



SEPTEMBER, 1883. 



THE GERM-THEORY OF DISEASE.* 



Bt Professob H. GRADLE, M. D. 



SCOURGES of the human race and diseases are attributed by sav- 

 ages to the influence of evil spirits. Extremes often meet. What 

 human intelligence suspected in its first dawn has been verified by 

 human intelligence in its highest development. Again, we have come 

 to the belief of evil spirits in disease, but these destroyers have now 

 assumed a tangible shape. Instead of the mere passive, unwitting 

 efforts with which we have hitherto resisted them, we now begin to 

 fight them in their own domain with all the resources of our intellect. 

 For they are no longer invisible creatures of our own imagination 

 but with that omnipotent instrument, the microscope, we can see and 

 identify them as living beings, of dimensions on the present verge of 

 visibility. The study of these minute foes constitutes the germ-theory. 

 This germ-theory of disease is rising to such importance in medi- 

 cal discussions that it can not be ignored by that part of the laity 

 who aspire to a fair general information. For it has substituted a 

 tangible reality for idle speculation and superstition so current former- 

 ly in the branch of medical science treating of the causes of disease. 

 Formerly that is, within a period scarcely over now the first cause 

 invoked to explain the origin of many diseases was the vague and much- 

 abused bugbear " cold." When that failed, obscure chemical changes, 

 of which no one knew anything definitely, or " impurities of the blood," 

 a term of similar accuracy and convenience, were accused, while with 

 regard to contagious diseases medical ignorance concealed itself by the 

 invocation of a " genus epidemicus." The germ-theory, as far as it is 

 applicable, does away with all these obscurities. It points out the 

 way to investigate the causes of disease with the same spirit of in- 



* A lecture delivered before the Chicago Philosophical Society, November 4, 1882. 

 vol. xxin. 37 



