244 E. I. WERBER. 



from just such intentionally, and still discernibly distorted, parts 

 of the iris. In several experiments Fischel observed besides the 

 formation of a lens from the pupillary edge of the iris small 

 double lenses, or twin (fused) lenses and in one case even three 

 lenses in other parts of the latter. For the formation of these 

 double (or multiple) structures Fischel, I think, correctly ac- 

 counts by close proximity to each other of two (or more) places 

 of injury. 1 Even the size of such lens-like structures he regards 

 as dependent upon the extent (number of cells) of the injured area. 



The lens formed by the pupillary edge of the iris after exstir- 

 pation of the primary lens is usually as large and as well differen- 

 tiated as the latter. This, according to Fischel, is due to the 

 circumstance that on extraction of the lens a large area comes 

 under the stimulus of the injury, and also to the fact that the 

 pupillary margin of the iris being an epithelial fold, it affords the 

 best means for the formation of a lens-bud (the "Knoten"- 

 Wolff '95), the first step in which is always a folding of the 

 corresponding part of the epithelium. 



Another apparent confirmation of this " Reizhypothese " was 

 furnished by the lentoids of the retina. The latter were observed 

 by Fischel ('02) in many experiments in which owing to the 

 extraction of the lens the eye bulb sustained accidental injuries. 

 The experimental test intentional injury of the retina again 

 gave positive results. The "retinal lentoids" could be demon- 

 strated to be due to transformation of thus injured cells or groups 

 of cells of the retina into such lens-like structures. The fact that 

 only the latter and not fully differentiated lenses of large size can 

 be formed by the retina on mechanical stimulation is, according 

 to Fischel, accounted for by the small area of such stimulation 

 and by the difficulty of forming a large fold. 



This ability of the retinal cells to become transformed into 

 lens-like structures Fischel regarded already in 1902 as no more 

 surprising than, (as demonstrated by his experiments), that of 

 any part of the iris, or of the epithelium of the skin in normal 



1 In some experiments of Wachs (/. c.) in which a fragment of the iris was intro- 

 duced into the posterior eye chamber of another animal whose lens has been 

 extracted, both the implanted fragment and the animal's own iris formed a lens. 

 In some of these cases where the fragment coalesced with the iris, two more or less 

 fused lenses were observed at the point of coalescence, one formed by the foreign 

 fragment and one by the iris. 



