NUNNELEY, ON THE RETINA. 219 
and that one microscopist should find appearances which 
others have not. Hence, notwithstanding the careful labours 
of many of the most eminent anatomists and observers, it is 
very doubtful if we are yet in possession of the real living 
structure of all the parts in this wonderful tissue. Certain 
I am that many statements are incorrect, that post-mortem 
changes have been confounded with normal living forms, 
and alterations effected by reagents have been described as 
natural conditions. Thus, while it is easy to say that some 
of the descriptions are certainly not correct, it is by no 
means so easy to feel certain that one’s own observations, 
however carefully and repeatedly made, are not also open to 
error. While, therefore, I have taken all the care I can, and 
spent much time upon the investigation, I would wish to be 
understood where differmg from other anatomists in the 
description of these parts, as doing so with the greatest 
deference, and with the full recognition of the weight 
attached to their skill and experience in the use of the 
microscope, and as only stating that which I believe to be 
the forms during life of these minute structures, and not as 
asserting dogmatically what is incapable of dispute.* 
The retina consists of several layers superimposed upon 
each other ; commencing externally, these are— 
* | believe the only way to examine the retina unchanged is to do so 
immediately after death, and without the addition of axy substance whatever. 
So rapidly do the rods undergo change, that in a few hours they are com- 
pletely altered; and not unfrequently even when taken from the living eye, 
they are seen to alter while under examination. IL know of no fluid which 
does not more or less change them. Even chromic acid, which Kolliker so 
extols, is not without greatly modifying influence upon the true retinal 
elements; and water émmcediately materially alters, and soon quite destroys 
the rods, and alters the granules and bulbs. It is extremely difficult pur- 
posely to make a section sufficiently thin in the fresh retina to examine it 
im profile; and, if expanded and dried, it requires maceration to render it 
fit for examination, by which the structures swell and alter irregularly, 
whatever fluid be used, so that the natural forms are not obtained; but 
these examinations are important as helping the inquiry, and by employing 
different fluids the one error may to some extent correct the other. The 
fluid which I have found to preserve the retina in the most natural condition 
for the longest time, is Goadby’s solution, No. 1, diluted by one half. My 
experience Of chromic acid is much less favorable than | had been led to 
expect by the statement of Kolliker and others. It is true it renders the 
cerebral elements of the retina, the nerve-fibres, the nucleated cells, and the 
granules or granular cells, more distinct; but its action upon the rods and 
conoidal bodies is very considerable—if strong, there is one confused fibrous 
mass, coloured yellow by the acid; if much diluted, the rods break up into 
dises and granwes, and the cones soon swell and disintegrate as with water. 
I doubt if its action be greatly superior to that of diluted acetic acid, which 
has the advantage of being colourless. 
