1914] Lafayette B. Mendel 169 



the replacement of a lost part, but also the development of a new 

 whole organism, or even a part of an organism, from a piece of an 

 adult, or of an embryo, or of an Q.gg. We must include also those 

 cases in which the part replaced is less than the part removed, or 

 even different in kind. . . . The term ' physiological regeneration ' I 

 shall use in the ordinary sense to include such changes as the moult- 

 ing and replacement of feathers, etc. — changes that are closely re- 

 lated to the life cycle of the individual." The power of regenera- 

 tion in the general sense diminishes as we ascend the vertebrate 

 Scale. Morgan believes that at least one reason for this lies in the 

 lack of coördinate regeneration in the higher vertebrates, i. e., the 

 slowness of certain tissues to regenerate in time with the other 

 tissues. Inasmuch as this has an indirect bearing upon the possible 

 causes of the uncorrelated growth which manifests itself as a path- 

 ological phenomenon at times, it may be worth while to quote 

 Morgan's view in some detail. He writes : " The evidence indi- 

 cates, I think, with some probability, that the failure is due to the 

 fact that the different tissues have very different rates of regenera- 

 tion. In other words, each tissue in man seems to possess the power 

 to regenerate its kind, but not all at the same pace, hence they fail 

 to coöperate at the proper time to form a new structure. In man 

 the skin regenerates; the muscles regenerate, though less well, per- 

 haps; the nerves and the blood vessels regenerate, and the bones 

 even have a not inconsiderable power to mend and even to some 

 extent to regenerate. Hence, as I have said, the failure of the new 

 limb to develop does not appear to be due to the failure of the indi- 

 vidual Clements to regenerate, but is due to their failure to regen- 

 erate concurrently. The bones or the ner^^es or the muscles may be 

 the main cause of the trouble, for they produce new material with 

 great slowness." 



The entire field of the physiology of repair is largely unexplored 

 as yet. Losses due to simple inanition can apparently speedily be 

 made good. Whether the end result as regards the composition of 

 the restored tissues is the same as that pertaining in normal growth 

 remains to be seen. If it is true that the capacity for regeneration 

 implies a latent youthfulness the extent to which loss in weight is 

 compatible with continuation of life may in part be dependent on 

 the latent power of growth as well as repair. Practically this finds 



