218 LESLIE B. AREY 



somewhat tedious, ])roccdure consisted in j^aring away the front 

 face of the eyeball with a razor after the eye had previously been 

 imbedded in paraffine. After removing the face of the eyeball 

 slightly beyond the ora serrata, the lens was pried from its 

 paraffine matrix with a dissecting needle; following such manipu- 

 lation reimbedding was of course necessary. The second and 

 simpler method was to remove the face of the eyeball with fine 

 curved scissors after the eye had been hardened in absolute 

 alcohol; unless, however, the eye was sufficiently hardened and 

 the greatest care exercised, the retina proper easily separated 

 from the pigmented epithelium. On the whole, the first method 

 was preferred to the second because of the wrinkling of the retina 

 that usually accompanied the use of the latter. 



Sections were cut 7^t to lOju thick, and only those passing 

 through the region of the optic nerve were retained for examina- 

 tion. Preparations were stained with Ehrlich-Biondi's triple 

 stain or were double stained in Heidenhain's iron haematoxylin 

 and a plasma counterstain. Ehrlich-Biondi in some instances 

 gave excellent differentiation of all elements, while at other 

 times it would show the capriciousness for which it is notorious ; 

 iron haematoxylin gave uniformly good preparations. 



When it became necessary to bleach the pigment, in order to 

 study the visual cells, which would otherwise be masked by the 

 partially or completely extended processes, the method employed 

 was essentially that of Mayer, in which nascent oxygen- is the 

 effective agent. 



EXPERIMENTAL PART 



a. Experimentation upon Ameiurus 



Ameiurus is well adapted for operations involving the optic 

 nerve. The soft skin and the relatively small eye allow easy 

 access to the orbit without causing the serious disturbance and 

 shock that is almost unavoidable when operating on fishes which 

 have eyes set in prominent bony sockets. 



2 When potassium chlorate and hydrochloric acid interact, it is commonly 

 said that nascent chlorine is the agent causing bleaching. As a matter of fact 

 the reaction libei'ates free oxygen. 



