472 Proceedings of the Eoycd Physical Society. 



like an ordinary tubercle nodule to the naked eye. At the 

 opposite margin of the ulcer is a similar but smaller nodule, 

 about ^ in. in diameter. Microscopic examination of a 

 small portion- of the thickened margin of the ulcer disclosed 

 a condition almost identical with that observed in gummata 

 and allied degenerated masses of tissue. Where the cheesy 

 <jondition is not well marked, the bundles of muscular fibre 

 are separated by numerous small round cells, almost like 

 those met with in granulation tissue. The muscular fibres 

 themselves are somewhat atrophied, and are frequently 

 divided into comparatively short lengths ; between them 

 small collections of granular material, and here and there 

 large well-formed cells, some of which have more than one 

 nucleus, are found. These cells are very like the endothelioid 

 cells so frequently met with in all tissues where there is any 

 tendency to fibrous tissue formation. 



The most important changes, however, are observed in the 

 blood vessels, and in order to make these changes more 

 comprehensible it may perhaps be well to describe very 

 briefly the structure of a blood vessel of a fish. 



As in a vessel of the human subject there are three coats : 

 the Tunica adventitia, or outer coat (PL XXIV., Fig. 3 a), 

 which in this position is of very considerable thickness. It 

 consists essentially of a dense network of connective tissue, in 

 which are a few nucleated cells. This connective tissue coat 

 may be said to be continuous with tliat of the surrounding 

 tissues, and any morbid process taking place in the one, 

 will in all probability be continued into the other. Within 

 this outer coat is a well-marked middle coat, or Tunica 

 medio. (Fig. 3 h), composed for the most part of circular 

 bands of non-striped muscular fibres. Within this middle or 

 muscular coat there is a distinct line of demarcation between 

 it and the internal coat, or Tunica intima. 



The internal coat is composed of two layers : — first a 

 layer of flattened connective tissue made up of laminae of 

 fibrous tissue, between which, usually seen in section as 

 spindle-shaped cells, are flattened branching connective 

 tissue cells. Inside this is a layer of flattened endothelial 

 cells, which forms the smooth glistening lining of the vessel 



