Caseous Ulcer in Skin of Cod. 471 



cod, which, says Mr Peach, " was evidently in very poor con- 

 dition. There were ulcerated patches on the same side, one 

 of them, ahout two inches in diameter, in a line with the 

 pectoral fin and a few inches behind it. . . . There were 

 several other smaller ulcers nearer the tail." 



The portions sent to me were placed at once in MUller's 

 fluid, in which they were exceedingly well preserved, until 

 I had an opportunity of examining them. 



On examining the fin and tissues over the pectoral arch, 

 which have been cut away with the fin, a large ulcer is seen 

 in the fold of the skin on the extensor surface of the joint. 

 It measures 1\ in. in diameter from above downwards, 2 in. 

 from before backwards, and extends over the upper three- 

 fourths of the breadth of the fin at its base. The ulcerating 

 margin is soft, friable, and caseous or cheesy looking. 



This cheesy margin is about three-quarters of an inch in 

 breadth, the free margin being much more granular and friable 

 than the attached portion, which is somewhat more cheesy 

 and tenaceous in consistence. 



The lower border of the ulcer is very considerably 

 thickened, is not caseous throughout, but is gelatinous. In 

 the gelatinous mass is embedded a peculiar caseous nodule. 

 A small piece of this was removed and examined under the 

 microscope, the result of which examination is given below. 

 In the floor of the ulcer itself the bones of the pectoral arch 

 and the bases of the fin rays are completely bared, as not 

 only is the pereosteum removed, but the ligaments and the 

 whole of the structures round the articulations are completely 

 disorganised, so that the proximal ends of the fin rays are 

 quite free. There are still small fragments of caseous 

 material scattered over and attached to the bones, these 

 pointing to the fact that caseation probably preceded the 

 ulceration in the whole area. At the tip of the fin is a 

 similar but smaller ulcer. Near the larger ulcer, but not 

 involved in the caseous margin, are a couple of small round 

 nodules, one of them -^V in. in diameter, with a raised, 

 slightly umbilicated centre, and a depressed margin. This 

 tubercle is not cheesy, but is dark brown in colour and 

 slightly gelatinous in the centre, though it is certainly not 



