THE 



POPULAR SCIENCE 



MONTHLY, 



JULY, 1909 



NATUKAL KESISTANCE TO INFECTIOUS DISEASE AND 



ITS KEINFOKCEMENT. 1 



By Dr. SIMON FLEXNER 



ROCKEFELLER INSTITUTE FOR MEDICAL RESEARCH 



COMMON observations early indicated that individuals of all animal 

 species, and of the human species especially, were very unequally 

 subject to disease. This elementary fact is impressed every day upon 

 the thoughtful and has been, from the earliest times, the object of much 

 ingenious speculation. Even to-day, and in spite of the acquisition of a 

 wealth of new facts in physiology and pathology, we are not able to 

 define fully the conditions that make for or against disease. How- 

 ever, the new knowledge which has been acquired enables us to see much 

 more deeply and clearly into the complex mechanisms of disease than 

 could be seen half a century ago ; but unfortunately our insight has not 

 been strengthened as regards all diseases, but almost exclusively in re- 

 lation to the infectious diseases. In respect to the other class, or non- 

 infectious or chronic diseases, among which are Bright's disease, vas- 

 cular disease, malignant tumors, the gains in fundamental knowledge 

 are far less great. 



It may be axiomatic to state that all actual progress in unraveling 

 the complicated conditions of disease depends upon precise knowledge 

 of its underlying causes; and yet in an age in which comparative 

 ignorance still requires that a certain amount of practise shall be 

 empirical, it is well to bear in mind this notion, so that what is under- 

 taken through knowledge may be kept distinct from what is adventured 

 through ignorance. It has been to the lasting credit of the medical 

 profession of an early period, when actual knowledge of the under- 

 lying causes of disease had not, and in the then state of development 



1 Read at the University Lectures on Public Health at Columbia University, 

 New York City, March 1. 



