DEVELOPMENTAL MECHANICS. 185 



the effects of hunger, protracted fever, chronic poisoning, or of 

 any other chronic disturbance like paralysis, etc., a useful ex- 

 termination of cells, hitherto unnoticed by pathologists, always 

 takes place an extermination, the magnitude and extent of 

 which depends upon the still unknown magnitude of qualitative 

 variations among the like cells of a single organ. Under such 

 circumstances the pells which happen to be least able to resist 

 the noxious influences must ceteris paribus be the first to 

 perish, and for this very reason after these cells have been 

 supplanted by the offspring of qualitatively more resistent 

 cells, the whole organism, or in the case of local affections, 

 the organ in question, must have become better able to resist 

 these particular noxious influences. (This does not exclude 

 the possibility that in special cases the resistance may be at 

 the same time diminished by other factors.) By means of hun- 

 ger, e.g., the organism is transformed by a process of selection 

 into a saving machine, because those cells which require much 

 nutriment will be the first to starve. Such an internal selec- 

 tion must also occur among the variations in nourishment and 

 activity during the course of normal vital processes, but to a 

 considerably less extent and in a manner more difficult to 

 determine ; hence we may expect that these conditions will be 

 first elucidated in pathological cases of a grosser character. 



Since, moreover, pathologists, representing as they do the 

 science of phenomena which are to a considerable extent 

 normal though occurring under abnormal conditions, take a real 

 interest in learning to comprehend normal modes of formation, 

 it will probably be the case in future more often than at 

 present, that these investigators will experiment with the 

 express purpose of ascertaining and analyzing normal modes of 

 formation. This has already been done with success by 

 surgeons in the case of the modi operandi of bone-formation. 



The "ArcJiiv fur Entwickelungsmechanik" will be glad to 

 welcome every such contribution from clinicians and comparative 

 anatomists. 



The advantage that will accrue in the first instance to devel- 

 opmental mechanics from such contributions will revert to the 

 service of the clinical disciplines, when once the modi operandi 



