160 Proceedings of the Royal Irish Academy. 
the centre till it attains the seat of injurj^, and finally the marginal 
parts become again transparent and the stellate corpuscles are again seen 
as they were before the inflammation, and uninjured by the stream 
of leucocytes which has passed over them. An accumulation of pus 
corpuscles never commences around the seat of injury except in cases 
where the substance of the cornea has been opened either by the sepa- 
ration of a slough after cauterisation, or when a portion of the membrane 
has been excised or punctured. Under these circumstances a grey 
opacity is observed to form about the seat of injury and, extending 
centrifugally, to join that spreading centripetally from the margin. 
This is explained by the creeping into the cornea, through the loss of 
substance, of wandering pus cells from the conjunctival sac. But when 
the injury to the cornea has not been such as to open its substance, any 
cloudiness observed at an early period around the seat of injury is due, 
not to the presence of pus, but to a staining of the epithelium and 
intercellular substance by the caustic, and to the granular degeneration 
of the stellate fixed corpuscles. 
Having by these observations proved that the corpuscles of pus did 
not originate in the cornea, but got into it from without, Cohnheim 
proceeded to investigate from what source they were derived — whether 
from the lymphatics or from the blood-vessels; and he concludes in 
favour of the latter for the following reasons. "When finely divided 
particles of insoluble colouring matter are injected into the lymphatic 
sacs of a frog, and a keratitis subsequently excited, many of the pus 
corpuscles found in the cornea are seen to contain coloured granules ; 
and this occurs whether the colouring matter is injected into a lym- 
phatic space near the head or at a distant part of the body. Further- 
more, it takes place if the colouring matter is injected directly into the 
blood, and in all cases after an injection into the lymph spaces, the 
white corpuscles of the blood are found in great numbers, containing 
coloured particles ; and the latter, after a short time, are never found 
free in the blood or tissues, but always enclosed in leucocytes. As a 
still further proof that the pus comes from the blood, the following 
curious experiment is adduced :— A frog had a large vein opened, and 
through this the blood was completely washed out of his body, and 
replaced by a weak saline solution. After this operation Cohnheim has 
succeeded in keeping the animals alive for some days, and when, under 
these circumstances, the cornea was cauterised, no pus was ever formed, 
but the tissue remained clear and transparent. 
A subsequent series of experiments was performed on the tongue of 
the frog with the same result. The pus was seen to be entirely derived 
from the emigrated white blood corpuscles, the connective tissue cells of 
the inflamed part undergoing no change. 
This short and imperfect account of Cohnheim' s investigations may 
give some idea of the beauty and ingenuity of the experiments. The 
pleasant and easy style in which the papers are written, and the 
novelty of the views put forth in them, make the whole subject one of 
peculiar interest ; and I confess T went to work at it with a strong 
