42 ADAPTATION AND DISEASE 



which wander out on to the mucous surfaces, take up bacteria 

 of various orders, and wander back again into the tissues — a 

 process which leads to the gradual habituation of the organism 

 to the dissociation products of the bacteria thus incepted, or 

 in other words, to a progressively increased capacity to dis- 

 sociate and digest the bacteria. Now, where immunity is already 

 established, anaphylaxis (the preliminary stage, as I have pointed 

 out, in the process) cannot be redeveloped. 



Accepting these very striking studies of Thiele and Embleton 

 — and as I have pointed out they gain confirmation from the 

 independent observations of several observers — we see how from 

 time to time infectious or epidemic diseases may arise de novo 

 through the evolution of more specialized pathogenic forms 

 from the more widely diffused saprophytic micro-organisms 

 growing upon the surfaces of the body. We can understand, 

 for example, how it was that Diphtheria came into prominence 

 only at the beginning of last century, when Bretonneau of Tours, 

 Napoleon's great army doctor, afforded his classical description. 

 It is impossible to believe that a disease with such obvious 

 clinical manifestations and such sharply-cut features should have 

 been present infecting man from the beginning of history with- 

 out a single physician in all the centuries recognizing and describ- 

 ing the throat condition, or the rapid devastation set up by the 

 disease. Diphtheria gains its simplest explanation as being due 

 to the acquirement within recent times of virulent properties by 

 some previously harmless diphtheroid bacillus growing in the 

 throat and upper respiratory passages. And so it has been with 

 Syphilis, with " Trench shin," Trench fever, Sweating sickness, 

 and, if with these, then with infections in general. 



I admit that there may be contributory causes, that particular 

 environments may favour the origin or reappearance of particular 

 diseases, as again that local tissue environment may determine 

 particular selective development of virulence. As regards the 

 former we have the remarkable history of Epidemic War 

 Nephritis, so well brought out at a recent meeting of the Medical 

 and Therapeutic section of the Royal Society of Medicine, with 

 its first known appearance in North America as an epidemic 

 beginning in the spring when, during the War of the Rebellion, 

 the campaign in the central region became a matter largely of 

 trench warfare ; the absolute disappearance of this particular 



