5A HIS, ON THE CORNEA. 
also by the aqueous humour, having shown experimentally 
that the cornea is permeable to the latter fluid. 
Such being the structure of the cornea, the author next 
inquires what are the changes which take place in that 
structure when some irritant adequate to produce inflam- 
matory action is applied to the part? The ordinary notion 
is, that the capillaries bordering the cornea throw out an 
exudation of plastic lymph into its substance ; and that this 
exudation, becoming more or less organized, gives rise to that 
obvious opaque substance which is the well-known ordinary 
consequence of corneal inflammation. In this, the current 
view of the inflammatory process, it will be observed that the 
tissue in which inflammatory action takes place is regarded 
as entirely passive, the inflammatory exudation being as much 
parasitic in the pre-existing tissue, as a mass of moculated 
cancer-cells would be, and wndergomg its changes as 
independently of everything but its feeders, the vessels. 
Virchow, however, has drawn attention to the circumstance 
that many so-called exudation-products are nothing but 
the local tissues metamorphosed ; and Dr. His’s investigations, 
carrying this idea further, tend to the conclusion that in 
ordinary traumatic keratitis the apparent exudation is entirely 
the product of a metamorphosis of the local tissues. 
This conclusion is so important, that it will be well to lay 
before the reader some of the details of the experiments 
on which it is based. The irritant employed by Dr. His in 
these investigations varied in character ; nitrate of silver, a 
hot wire, excision of small portions, the introduction of 
threads which were allowed to remain—but the results were 
always essentially similar. The irritant was invariably applied 
in the centre of the cornea, and at first its effects were more 
prominently visible throughout a wedge-shaped area, whose 
base was peripheral, its apex at the pomt irritated. To this 
area Dr. His applies the name of “ Reiz-bezirk,” or “ area of 
irritation.” The actual spot to which the irritant is applied 
may be termed the “ point of irritation.” 
«The cornea of a rabbit which has been subjected to intense traumatic 
irritation presents but little change to the unassisted eye halfan hour after- 
wards; but the microscope already reveals distinct histological changes. 
In the first place the superficial cells, especially those of the area of irritation, 
are obviously ene ies In contradistinction from their normal appearance, 
the body of the cell is well marked, and has remarkably granular contents. 
The nuclei are bright and sharply defined, without visible nucleoli, and are at 
once remarkable for their irregular and unusual forms. Having a general 
direction parallel with the cell, they are mostly more or less angular, instead 
of being round or oval; they are notched, or constricted, or horseshoe- 
shaped; they grow out on one side as though they would form buds, or 
