Physiological Basis of Restitution of Lost Parts 497 



the other parts C, D, E are plastic, i. e., if their activities are 

 readilv^ and rapidly altered by altered conditions, they will be 

 affected by the decrease in ^^-correlations following the removal 

 of A and will undergo more or less change in response to the 

 changed correlations, i. e., regulation by what we ordinarily call 

 redifferentiation will occur. If, on the other hand the parts C, 

 D, E are relatively stable, i. e., not rapidly changed by altered 

 conditions, they and the correlations arising from them will remain 

 much the same as before the removal of y^. But the ^-processes 

 in B, G, F are out of proportion to these correlations and must be 

 quantitatively increased by them. In this case then equilibrium 

 is regained by functional hypertrophy of the portions oi' B,G,F, 

 which are the functional substitutes for J. This is what we know 

 as regeneration in the stricter sense, i. e., formation of newt;ssue 

 from the regions adjoining the cut surface and its visible differen- 

 tiation with increase in size into a part like that removed. In 

 most plants and in some animals regeneration occurs from regions 

 more or less distant from the cut surface, simply because these 

 regions are physiologically more like the missing part than is the 

 region at the cut surface. 



As a matter of fact, since correlations in the system are at least 

 in large measure mutual, most if not all cases of restitution 

 are mixtures of redifferentiation and regeneration. Some change, 

 i. e., some redifferentiation occurs in some or in all parts of the 

 system and some regeneration, i. e., functional hypertrophy of the 

 part which forms the physiological substitute for the part removed 

 takes place. 



Holmes' hypothesis fails to recognize the fundamental fact, 

 viz: that something must remain after the removal of a part, J, 

 which can take its place functionally in the system in some degree. 

 Without this the only factors which can prevent progressive depar- 

 ture from the original condition are lack of plasticity in the parts 

 remaining or one-sided relations between parts. As a matter of 

 fact however plasticity is a conspicuous feature in many forms in 

 which the regulation of parts into wholes occurs most readily, 

 and on the other hand all the evidence indicates that correlations 

 are in large measure mutual rather than one-sided. In those cases 



