62 H. M. BRRNARri. 



But these accumulations and the clottings of strands and 

 membranes are not sufficient to account for the lifelong 

 streamings of refractive matter into this layer, and we should 

 have to assume that it escaped finally through the internal 

 limiting membrane to join the vitreous humour, even if the 

 microscope did not clearly show us that this is what actually 

 takes place. 



In very few sections will the internal membrane be seen 

 quite thin and clear; it is usually found thick and apparently 

 laminated, and la^^ers are frequently found flaking off into 

 the hollow of the eye. That these flakes are, at any rate in 

 part, due to the matter which comes along the " Miiller's 

 fibres " can be seen in the fact that in osmic acid preparations, 

 in which these streams are usually blackened, the portions 

 of the internal membrane which cover their conical expan- 

 sions not infrequently show different degrees of blackening 

 (see fig. 29, a). This shows that the refractive matter is 

 certainly deposited on the internal limiting membrane. The 

 question is. Does it pass through ? It certainly passed into 

 the retina through the external protoplasmic membrane, 

 pushed out in the form of rods it traverses the whole thick- 

 ness of the retina, and if it does not pass through the exactly 

 similar protoplasmic membrane on the inside of the retina it 

 ought to accumulate in large quantities. The only accumu- 

 lations which we actually find in connection with this mem- 

 brane are the above-mentioned laminee, which, as is well 

 known, belong to the vitreous humour. Some sections, 

 indeed, show the stained " Miiller's fibres," looking like so 

 many processes rooting the similarly stained remains of the 

 vitreous humour into the retina. And hei'e let me say 

 that absolute microscopic demonstration of subtle physio- 

 logical processes may not be possible as so many separate 

 details, but when all the facts are taken together the evidence 

 may become as convincing as if we could prove each detail 

 separately. This particular detail, however, namely, that the 

 refractive matter absorbed by the rods passes ultimately into 

 the vitreous humour, admits of demonstration. 



