THE LENS-PROBLEM. 247 



seem, however, to leave no doubt that the lens contains some- 

 thing, some substance that apparently inhibits the formation 

 of another lens from the iris which would invariably occur in its 

 absence. 1 This substance, however, again need not necessarily 

 be secreted, in order to neutralize the action of the "lentogenic 

 enzyme." Just what the nature of this substance may be, is, of 

 course, altogether a matter of conjecture. It might perhaps be 

 imagined as an "antibody" ("antigen") contained in the periph- 

 eral part (the epithelial cells) of the lens and the realization of 

 its inhibiting action may be due to close contact of that part of 

 the lens with the epithelium of the iris. 



This "antibody" being, just like the lens, a product of the 

 "lentogenic reaction," we may perhaps in the case of the verte- 

 brate eye eventually have a striking example of some of the 

 factors (synthetic enzyme action Loeb, '16) concerned not 

 only with development and growth, but also with the limitation 

 of the latter 2 for the attainment of proper size relations, and with 

 the maintenance of a chemical equilibrium indispensible for the 

 undisturbed existence of a structure or an organ. 3 



1 Fischel ('16) has recently furnished another interesting example cf the ap- 

 parent chemical action of the lens which he also considers as a "secretion." He 

 transplanted in larvae (about 3 cm. large) of Salamandra maculosa the exstirpated 

 lens under the skin of various parts of the head or trunk. As a result he observed 

 that, while the lens underwent a gradual dedifferentiation and eventual absorption, 

 the skin above the transplantate showed remarkable changes. The unicellular 

 glands (the cells of Leydig) disappeared from the corresponding region of the skin, 

 which, owing to the morphological changes, by its appearance suggested a similarity 

 to "friihe Entwicklungsstadien des Hautepithels" (p. 37). Eventually this region 

 of the skin became transparent and was very similar to a fully differentiated 

 cornea. Similar observations were, as mentioned above (p. 242), recorded also by 

 Wachs (/. c.) on transplanting parts of a fully differentiated optic cup under the skin. 



2 The fact that the " regenerating " lens does not grow indefinitely (as it might, 

 if it were a benign tumor regarded as such at one time by Fischel, 'oo), but is 

 limited in its growth to attain just the size to fit the pupilla, has recently occasioned 

 J. Loeb ('16) to raise the question regarding the factors limiting growth. Ac- 

 cording to our assumption it might perhaps be imagined that every tissue (or 

 structure) elaborates during its development a substance (an "antibody") which 

 inhibits its growth beyond certain limits. In this case both growth and its auto- 

 matic limitation would be conditioned by the same factors of development. 



3 Fischel ('16) concludes from his experiments that the already fully differentiated 

 lens needs the chemical influence of the eye for its normal (undisturbed) existence. 



OSBORN ZOOLOGICAL LABORATORY, 



YALE UNIVERSITY, October 4, 1917. 



