413 
which reach the surface; they do not end there, but return 
towards the depth of the cornea. 
We come now to the second division of this part of our 
undertaking, that is, the nerves of the substance of the frog’s 
cornea. The results to which I am led by the investiga- 
tion of the same were obtained by the following methods. 
I must, however, first state that although very fine nerves of 
the frog’s cornea have been minutely described in fresh pre- 
parations, though chiefly in such as had been treated 
with gold chloride, they are not always and not so com- 
pletely to be made out by the ordinary method of gold pre- 
paration as in that now to be described. I pass a silk 
thread through the centre of the cornea of a healthy middle- 
sized or large specimen of Rana esculenta, and bringing 
it out again at the sclerotic ring, tie in it a loose knot to hold 
it fast ; in short, I proceed in the same way as one does in 
inflammation studies. After the thread has remained from 
five to eight hours in the cornea, I cut out the latter with the 
greatest care, allow it to remain from a quarter to half an hour 
in pure half per cent. solution of gold chloride, and place it 
then in distilled water so long as the action of the light lasts, 
that is, until it has obtained the well-known dark violet-red 
or red-brown colour, a space of time which varies according 
to the season from one to three days. Then I tear off from 
this the epithelium, together with a very thin layer of the 
corneal tissue, and enclose the remaining portion in glycerine. 
We must assume that the reader is too well acquainted with 
the characteristics of the corneal corpuscles, both the still 
normal, beautifully branched ones, as well as those exhibiting 
already some slight change, and the wander-cells present in 
some places sparingly, in other places abundantly, than that 
we need go into greater detail here concerning them.! 
' The controversy concerning the cells and plasmatic channels (Saft- 
kanalchen) of the cornea substance, which has been going on during 
the last few years, will, as well as the physiological and pathological cha- 
racters of the lymph system and the cellular elements of connective tissue, 
be treated at length on another occasion. Only one remark will here 
be made. Those who maintain that the sharply-marked, clear, branched 
figures, embedded in a yellowish-brown ground substance, which come out 
in a corneal tissue after treatment with silver, and which correspond to the 
well known beautiful branched flat cells with oblong flattened nucleus, pro- 
duced by gold treatment, do not represent the cellular elements of the 
cornea, but are occasioned by coagulation, fissures, or the like, in an inter- 
fibrillar albuminoid substance, and who take their stand upon this—that 
no one has yet succeeded, nor ever will succeed, in demonstrating in the 
silver figures the branched cellular elements,—these persons, I say, | would 
advise of the following facts. When the cornea of a living rabbit is rubbed 
with lunar caustic so long that a great portion of the interior epithelium is 
