72 WARFARE IN THE HUMAN BODY 



were definite responses, and it is easy to infer that before 

 response became rapid and easy every kind of disaster and 

 disablement must have occurred to those subjected to 

 reaction-provoking stresses. The very process of adapta- 

 tion (and on these lines "adaptation" is no longer a 

 mystic word) implies long periods of disordered function 

 and poor structural response even in those who survived 

 after repair. But now bone is so plastic and fluent that 

 when it is grafted the osteoblasts and osteoclasts use and 

 shape it according to the form of the main bone of which 

 it becomes a part. For, according to Keith, Wolff's law 

 may be more simply expressed if we say : " Osteoblasts at 

 all times build and unbuild according to the stresses to 

 which they are subjected." 



When we speak of repair it may be noted that the 

 treatises on this subject are strictly limited in their 

 purview. They mostly follow Hunter, a vitally important 

 figure in the history of pathology, and indeed of all medical 

 science, who, however, lacked the apparatus of knowledge 

 now at every one's disposal. We learn a great deal about 

 the repair of wounds and fractures : of the functions of 

 the fibroblasts or of the wandering cells of the blood- 

 stream, and are told, lately, much of regeneration ; but of 

 the evolutionary value of organized exudations we hear 

 little or nothing. Nor has it been suggested that it is to 

 this and analogous processes that much new structure is due. 

 That this is so is strikingly apparent, as I shall attempt 

 to show, in many organs of a highly specialized type. In 

 no structure, perhaps, is the process so clearly seen as 

 in the mammalian heart, which is a perfect museum of 

 evolutionary failures and dislocations, compensated for by 

 an extraordinary complication of patched-up tissues and 

 altered muscle in which, perhaps, one tissue takes on 



