MOVEMENTS IN THE VISUAL CELLS 125 



The technique of preparing retinas for microscopical examina 

 tion was very simple. Eyes were removed from their orbits 

 in two ways. In Ameiurus, where the eyes are prominent and 

 the skin is soft, excision was performed directly. The eyes of 

 amphibians and of fishes other than Ameiurus, particularly in 

 experiments conducted in the dark where rapidity of operation 

 was desirable, were not excised directly but according to the 

 following procedure. With heavy scissors the cranium was 

 bisected in a median sagittal plane; following this, a trans- 

 verse cut just posterior to the orbit freed the two halves of the 

 cranium, with the contained eyes, from the rest of the body. 

 In either case the operation was performed in a few seconds and 

 the eye, without being handled, was allowed to drop into the 

 fixing fluid. - 



Both Perenj'i's and Kloinenbcrg's fluids gave good fixation 

 (Howard, '08; Palmer, '12), but of the two, Perenyi was pre- 

 ferred. The toughness of the sclera and the consequent slow- 

 ness in the penetration of fluids demands generous allowances 

 of time during the various steps preparatory to imbedding in 

 paraffine. Dehydration and clearing in xylol should, however, 

 progress as rapidly as possil)le since otherwise the sclera liecomes 

 extremely hard. 



Two methods were used in removing the lens, one of which, 

 although longer, gave much more satisfactory results. The first 

 somewhat tedious procedure consisted in paring away the front 

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

 imbedded in parafline. After removing the face of the eyeball 

 slightl}^ l)eyond the ora serrata, the lens was pried from its paraf- 

 fine matrix with a dissecting needle; following such manipula- 

 tion 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 alco- 

 hol; if, however, the eye was not sufl^ciently hardened or the 



^ A method of simple decapitation used by Pcrgens has lieen criticized by 

 various workers who contend that slight changes occur in the position of the 

 retinal elements after the head is immersed in the killing fluid. In a series of 

 controlled experiments, however, I could detect no post-mortem disturbances 

 when the head was both bisected and cut from the trunk. 



