Physiological Basis of Restitution of Lost Parts 489 



of mutual dependence of the parts — factors of course which vary 

 in different org-anisms. But Child overlooks the fact that accord- 

 ing to the symbiotic relation assumed, the other cells C, D, E, etc., 

 tend to keep B, F, G in their original condition. In so far as these 

 remain in their original state, their influence on the indifferent 

 tissue in the region of A will tend to mold it in the direction of the 

 missing parts. In so far as B, G and F are modified through the 

 loss of the missing part, their influence on the tissue in the region 

 of y^ will come to be modified, and they will in turn modify the 

 cells lying next to them. But, as there is a tendency for the modi- 

 fications produced by the loss of ^, to spread successively to other 

 parts, there is also a tendency, according to my theory, toward 

 the checking and reversal of this process. If the loss of J tends to 

 modify B, F and G, the presence of £, C and D tends to hold them 

 in place, and in so far as these are maintained through this influence 

 they tend to mold the tissue in the position of A into the form of 

 the missing part; and in so far as this is so molded, its modifying 

 influence on B, F and G is diminished" (Holmes '07, pp. 425, 

 426). 



I am unable to see that this argument shows that something like 

 A may be generally replaced. Undoubtedly the modifying in- 

 fluence of A upon the contiguous cells or parts B, F, G, is lessened 

 by the presence of other cells or parts, E, C, D, but it is not reduced 

 to zero in any case where the relations between parts are mutual. 

 The balance between the "tendency for the modification produced 

 by the loss of ^ to spread" and the opposite tendency simply deter- 

 mines how great or how small the modification shall be. Some- 

 thing more or less like A may undoubtedly be produced in many 

 cases, but according to this hypothesis we should expect that the 

 regenerated part would diflPer more or less widely from the original 

 part in most cases. 



In fact, if the restoration of a part removed is purely a matter of 

 interrelation between the various parts ofthe system, we must modify 

 this hypothesis in either one of two ways to account for it. First: we 

 may assume that the removal of the part, A in Holmes' diagram, 

 does not alter the other parts, B, G, F, etc., in any way which 

 affects essentially their interrelations with the parts ofthe system. 



