206 KEG EN ERA TION 



if, in the absence of this part, the lens would develop from other 

 parts of the uninjured margin of the iris. He found that the new 

 lens still 'comes from the upper edge of the iris from the part left 

 after the operation and not from the intact edge in other parts. 

 This seemed to show that an injury to the iris is in itself a stimulus 

 that starts the formation of a lens. This conclusion is made prob- 

 able by the results of other experiments in which the iris was stuck at 

 several points, when new lenses began to develop at several of these 

 regions of injury. In some cases Fischel found that two or more 

 lenses began to develop when the iris had not been intentionally 

 injured; but it is not improbable that some sort of injury may have 

 been effected when the lens was removed. Fischel, as has been said, 

 removed extensive portions of the upper part of the iris and found 

 that a new lens could be formed at the cut-edge, even in the region 

 of the pars ciliaris ; and, even after the removal of the entire upper 

 part of the iris, lens-like structures may appear in the inner or retinal 

 layer of the remaining region. 



If instead of removing the lens it is displaced by pressing on the 

 cornea until the lens leaves its normal position and comes to lie in 

 the vitreous humor, a new lens develops from the edge of the iris, as 

 though the old lens had been entirely removed from the eye, but in 

 the experiments' in which this was done the new lens was not well 

 developed. The result shows that it is not necessary that the old 

 lens be removed from the eye in order to induce the regeneration of 

 a new one, but only that the lens lose its normal position in the eye. 



In regard to the stimulus that determines the development of the 

 lens, Fischel agrees with Wolff that gravity has a share in producing 

 the result. The absence of the old lens from its normal position, 

 as well as the wrinkling of the cornea, may also enter in as factors. 

 Fischel takes issue with Wolff as to the interpretation of the result 

 as an adaptation, and states that "the organism always responds to a 

 change of relation in only one way, whose direction is already deter- 

 mined by internal structural relations, without regard to whether 

 the result is adaptive or not. The response follows each stimulus in 

 a way determined by the limited possibilities of the cells. With 

 such a uniformity in the reaction, the idea of a fundamental adapt- 

 ability cannot be connected, since the reaction that appears to us to 

 be adaptive in a series of complicated changes may be non-adaptive 

 in another series." 



Whether Fischel has here really met Wolff's argument is, I think, 

 open to question. It does not alter the result to show that factors 

 already existing enter into the process, so long as the organism is so 

 constructed that just those factors are present that bring about a use- 

 ful response. That the response may be sometimes imperfect does 



