460 H. M. Bernard. 



present demonstration that the refractive matter within the 

 outer limbs is absorbed by the rods from the pigment, I 

 should like to mention two points on which I am in great 

 uncertainty. It has appeared to me more than once as if 

 the pigment granules could pass bodily into the rods, and, 

 at least for a time, maintain their individuality. I do not 

 see why this should not occasionally happen ; indeed, I cannot 

 explain some of the phenomena on any other hypothesis. 

 Still, the evidence shows conclusively that this is not the 

 normal method, but that the pigment granules are absorbed 

 as a colourless or nearly colourless refractive and amorphous 

 matter. The occasional finding of retinas in which the 

 colour of this refractive matter within the rod is the same as 

 that of the pigment granules without (I have seen this in 

 sections of the retinas of the pigeon and of frog tadpoles, 

 etc.) may be mentioned, in passing, as additional evidence of 

 the origin of the former from the latter. 



One appearance suggestive of pigment granules within the 

 rod seen in osmic acid preparations must be familiar to all 

 students of the retina. Itis the " disc^' formation on which 

 Max Schultze laid so much stress. I now, however, refer 

 this to a transverse flaking of the internal reticulum, perhaps 

 a kind of coagulation of the same, as Max Schultze himself 

 suggested. The transverse flakes are usually deeply coloui'ed 

 by osmic acid, and often appear exactly like layers of intruded 

 pigment granules. In preparations not treated with osmic 

 acid the appearance is not to be found. 



The second point is the relation of the phenomena here 

 detailed to the visual purple. This is said to be produced in 

 the dark through the interaction of the rods and the pigment 

 epithelium, i. e. when the epithelium is only in contact with 

 the tips of the rods, and, further, it is said to be bleached by 

 the light, i. e. when the rods should, according to my own 

 observations, be absorbing clear refractive matter from the 

 epithelial cells, which are then in intimate association with 

 the rods, inasmuch as tongues of the cells then travel up 

 between the rods. I am of course aware that it is frequently 



