736 William Patten 



structures observed iu retinas macerateti iu weak sulpburic acid. 

 This treatment usuali}^ eats off the euds of tlie rods. wbich first be- 

 come long-itudiually striated , or fibrous , leaviug tbe basai ends at- 

 tacbed to the retinophorae. Between the remnants of each rod, could 

 then be seen a short, conical projectiou, attaehed to the pseudo-mem- 

 brane. For a long time I regarded these structures, which showed great 

 reg'ularìty in shape and position, as a set of coues similar to those of 

 the Vertebrate eye, and belongìng to the long and slender retinophorae. 

 But by treatment with hot chromic acid the cones had disappeared, and 

 I finally discovered that they were produced by the sulpburic acid, which 

 coagulated the external uerve tìbres of the rods, eausing them to adhere 

 to the pseudo-membrane in the shape of the conical projections referred 

 to above. Ali reagents, applied in whatever manner, caused a dis- 

 arrangement of the rods, so that, in most cases, the whole retina was 

 drawn away from the sclerotica toward the centre of the eye, leaving 

 a larger or smaller space between the bases of the rods and the ar- 

 gentea. When hot chromic acid of CO" C, or picro- sulpburic acid of 

 the sanie temperature, was used, the effectwas nearly obviated, but on 

 tbe other band, the relations of the retina, lens etc., to each otber w^ere 

 greatly disturbed. In order to obtaiu the best preparations, with ali the 

 parts in the most naturai position, it is necessary to kill the eyes first 

 with VioVo chromic acid for V2 hour, then allow them to remain in 

 chromic acid, Y2V0 ^oi' 24 hours; '/lo'Vo for 24 hours; and finally '/.//o 

 for 48 hours or more^ Next to this method, I think that solutions of 

 sulpburic acid (20 drops to 50 grams) give the best preparations for 

 every thing except the rods. 



The double layer of the sclerotica, and the fibres penetrating it, 

 cau be seen iu sections of eyes treated for 24 hours in '/:)"/<) chromic 

 acid. Besides these methods almost ali the other reagents bave been 

 tried, in different combinations and at different temperatures, but 

 with poor results. 



Maceration and dissection. 



For Isolation of the pigmented epithelial cells, and the cells of tbe 

 cornea, weak solutions of Müller s fluid, or biehromate of potash, gave 

 excellent results. For the maceration of ali other Clements, I bave used 



' The smaller eyes of other species of Pecten are much more easily prepared, 

 but, on account of their small size, are not so good for study. 



