THE LENS-PROBLEM. 24! 



the case of the formation of the retinal lentoids? Considering 

 the fact that the retinal cells can both furnish the "lentogenic" 

 stimulus and respond to it, it would certainly seem not far fetched 

 to assume that the stimulus for the formation of the lentoids by 

 the cells of the retina issues from themselves. In this case the 

 retinal cells react to their own "lentogenic enzyme." Both the 

 conditions for furnishing the stimulus and the latent potency of 

 responding to such a stimulus are known to be present in the 

 retina. May not this double capacity underly also the formation 

 of the lens from the iris? 



To answer the latter question it would be necessary to find 

 out whether the iris besides its known potency of forming a lens 

 (Wolff, Miiller, Fischel, Wachs, and others) is also capable of 

 furnishing the "lentogenic stimulus," if in contact with epithe- 

 lium (or some other ectodermal derivative). Unfortunately, 

 however, the question cannot be answered definitely at the present 

 time. 



There exists only one experiment (by Wachs, /. c., p. 430 and 

 Figs. 46, 47, 48 and 49) which suggests this possibility, but the 

 conditions in this experiment are not quite clear. A fragment 

 of the iris was in this case (No. 39) transplanted into the car- 

 tilaginous capsule of the otic labyrinth. This fragment stimu- 

 lated the formation of a lens (Fig. 49) from a strand of epithelium 

 that had grown in from the edge of the wound. It is uncertain, 

 however, whether in this case the "lentogenic" stimulus issued 

 from the iris or perhaps from retinal cells contained in the trans- 

 planted fragment. For while on p. 429 Wachs states that this 

 fragment was "ein Stuck der oberen Iris" and that "nach 28 

 Tagen . . . war das Stuck mit Goldpigment noch deutlich 

 sichtbar," on p. 447 (in the summary) he refers to it as "ein 

 Stuck des Auges" and in the record (p. 423) this case (No. 39) 

 is enumerated among those in which "ein Stuck des oberen 

 Augenteiles" was transplanted into the labyrinth. Wachs 

 himself, however, does not state whether he assumes that in this 

 case the regenerated epithelium formed the lens under the in- 

 fluence of retinal cells or of the iris. 



There is no reason, however, why the latter possibility should 

 be excluded. It is certainly not excluded by those experiments 



