His, ON THE CORNEA. 53 
We must omit more than a passing reference to the chemical 
properties of the cornea; to its permeability by the aqueous 
humour ; and to its early structural condition ; on all of which 
points much valuable information is given by Dr. His. 
With regard to the nerves discovered by Schlemm, nearly 
thirty years ago, Dr. His states that, very soon after their 
entrance into the cornea they lose their dark contours and be- 
come pale and nucleated fibres. These fibres divide repeatedly, 
and at length anastomose with one another, so that their ul- 
timate termination here, at any rate, is in a nervous network. 
This is a very important fact, and one whose confirmation is 
highly desirable. The nerves are almost entirely confined to 
the anterior third of the thickness of the cornea, none at all 
apparently reaching its posterior half. In conformity with 
this anatomical fact, Dr. His found that im experimenting on 
rabbits the animals struggled violently when the heated wire 
which he employed came into contact with the cornea, and 
more especially as it entered its substance ; but that no further 
signs of pain were manifested as it passed from this point to 
the membrane of Descemet. 
Capillary vessels are commonly found to extend mto the 
human cornea for a distance of from half a line to a line from 
the margin; and it has been supposed that the corneal cells 
and their processes are hollow, and that they form a system 
of tubes communicating with one another and with these 
vessels. With regard to the first point, Dr. His decides in 
favour of the tubularity of the corneal cells and their 
processes —influenced. chiefly, as it would appear, by the 
results of touching the cornea of a rabbit or of a goat with 
nitrate of silver. The white spot which is immediately 
formed is found, on microscopic examination, to consist of 
granules of metallic silver, which are deposited only in the 
cells and their processes—the intercellular substance merely 
acquiring a slight brownish tinge. Furthermore, the deposit 
of metallic silver is not confined to those cells which are in 
the immediate vicinity of the spot touched, but is found in 
other and quite isolated ones. We cannot see in this curious 
experiment, however, any proof of the tubularity of the 
corneal cells and processes. If they were solid the same 
thing would occur, so long as they were capable of absorbing 
fiuid and contained more chlorides than the surrounding 
substance. 
On the other hand, im opposition to Coccius, Dr. His 
maintains that no communication exists between the cells 
and; the capillaries. And he conceives that the nutrition of 
the cornea is kept up not only by the vascular supply, but 
