THE EYE OF PECTEN. 53 



rods — truly a marked advance in the knowledge of the eye- 

 structure. 



Technique. 



This investigation of the eye has been carried out by the 

 study of sections (paraffin and paraffin-celloidin), by macera- 

 tion pi'eparatious and by the teasing of fixed material. 



It is impossible to over-estimate the value of macei-ations in 

 conjunction with section work, and the true shape of many 

 cells could not have been determined without this method. 

 For both fixation and maceration it was found that diiferent 

 reagents were necessary according to the cells to be studied. 

 In the retina alone the various elements reacted very differently 

 to fixatives and macerating fluids, and it was surprising to 

 notice how different the preservation of the different cells 

 might be after treatment with the same fixative. 



The fixatives giving the best general fixation of all parts 

 were Zenker's fluid and Carnoy's mixture. Zenker was used 

 as follows : Fixation lasted for about twelve to twenty-four 

 hours, and was followed by washing first with water and then 

 in alcohol of gradually rising strength. Sections were made 

 after paraffin embedding, the usual thickness being that of 

 the rod-cells, namely 6 n, but others were only 2 fx, and some 

 were 10 fx thick. The stains used after Zenker were Mallory 

 (connective-tissue stain), iron hematoxylin (Heidenhain), a 

 modified Weigert, and picric acid — saurefuchsin. 



Mallory's connective-tissue stain. — The sections, 

 on slides, were stained in an aqueous solution of saurefuchsin, 

 0*05 per cent., for ten minutes, then rinsed quickly in water 

 and placed in 1 per cent, solution of phosphormolybdic acid 

 for three to five minutes. After washing in several changes 

 of water for five to ten minutes the sections were stained in 

 the following solution for eight to fifteen minutes : 



Aqueous aniline blue (Griibler) . . 0*5 gr. 

 Orange G. ..... . 2*0 gr. 



Oxalic acid ...... 2*0 gr. 



Water 100*0 c.c. 



