Caseous Ulcer in Skin of Cod. 475 



some similar change ; it becomes hyaline, swollen, then granu- 

 lar ; and at this stage takes on the yellow picric acid stain of 

 picro-carmine. Around the central hyaline or caseous clot, 

 the thickened inner coat may be distinguished for some 

 time, but eventually the cells in this position begin to 

 swell up, they gradually become hyaline, run together, and 

 then assume a granular appearance, taking on the charac- 

 teristic yellow stain, to which reference has already been 

 made. The vascular supply has been cut off not from the 

 walls of the vessel only, but also from the areas which were 

 supplied by these vessels. Hence we see in the cut specimen 

 large tracts of tissue in which the cells are hyaline, swollen, 

 and in many cases running together, just as we have seen 

 them in the walls of the vessels. The fibres are also swollen 

 or granular, so that large homogeneous or granular masses, 

 stained yellow with picro-carmine, are seen, corresponding 

 in their distribution with that of the obliterated vessel. 



It is in consequence of these changes that the ulceration 

 described takes place. The degenerated tracts get larger 

 and larger, they gradually run together, and the soft granular 

 material disintegrates, leaving ulcerated patches, which in 

 turn get larger and run together to form ulcers of the size 

 detailed at the commencement of the paper. The processes 

 mentioned above as preceding the ulceration are of course 

 best marked at the margin of the ulcer, the advanced caseous 

 patches at the extreme margin and the inflammatory changes 

 some little distance away from this point. 



The process of caseation is very similar to that observed 

 in the conditions associated with tubercle, syphilis, and the 

 like, and the results as seen under the naked eye are very 

 Like one another. 



It should be observed, however, that here there are no 

 giant cells. Taking one of the vessels as an example, there 

 is the well advanced caseous clot in the centre, surrounding 

 this are endothelioid cells or plates lying on a species of 

 reticulum, both cells and fibres growing in connection with 

 the laminated layer of the inner coat of the vessel. Even 

 in the degenerating areas outside the vessels altogether, not a 

 single giant cell could be made out. 



