PREFACE 



WHEN at the beginning of the Great War the invitation was 

 tendered to me to deliver the time-honoured Croonian Lectures 

 before the Royal College of Physicians of London, it was long 

 months before I could determine my subject. During these 

 months the burden of administrative work in connection with the 

 Canadian Army Medical Service became progressively greater. 

 Research in the laboratory was out of the question. My official 

 duties at that period dealt largely with returns and statistics 

 of invalidism, but soon it became apparent that months, 

 if not years, must elapse before the vast mass of material 

 being collected by the Medical Research Committee at 

 the British Museum would be fully available. Inevitably, 

 therefore, I was led to fall back upon previous studies, 

 and, when still debating, a chance discussion with a leading 

 British biologist convinced me that the time was ripe to 

 bring together and sum up the conclusions regarding Adapta- 

 tion which as a student of pathology I had reached gradually 

 in the years preceding the War. I judged from the discussion 

 above referred to that that earlier work was not known to 

 biologists in general. Varied as is his reading and brilliant his 

 memory, this distinguished biologist was evidently wholly ignorant 

 concerning it. It seemed also that it would be serviceable to 

 present the conclusions reached, not so much from the point 

 of view of their medical bearing, as from that of their biological 

 significance, in order that both morphologist and physician might 

 observe the direction in which medical research is surely leading 



