Caseous Ulcer in Skin of Cod. 473 



(Fig. 3 c). The vein differs from the artery in that the mus- 

 cular coat is very much thinner, and the outer coat is usually 

 not so well developed. 



On examining the vessels in the area above' mentioned 

 (the small piece taken from the thickened margin of the 

 ulcer), the following appearances are present. As one would 

 expect from the infiltration already observed in the con- 

 nective tissue between the bundles of muscular fibre, there 

 is marked infiltration of the outer connective tissue coat 

 with small round cells. These small cells consist almost 

 entirely of a nucleus, the film of protoplasm around them 

 being very thin indeed. There are, however, along with tlie 

 small cells, a number of large, well-formed, usually rounded 

 connective tissue cells, in which the formed material around 

 the nucleus is present in considerable amount. Some of 

 these cells have several nuclei. 



The muscular coat is as a rule not much altered, but 

 occasionally one finds a slight increase in the number of 

 small round cells in this position. 



It is on the internal coat, however, that the most marked 

 changes are seen; in the present instance it is enormously 

 and irregularly thickened. In the thickened portion the 

 laminae are arranged apparently not in the same plane as 

 the circumference of the vessel but at right angles to it, and 

 the cells seen in section as they lie between the laminae, run 

 with their long axes at right angles to the plane of the 

 circumference. A similar arrangement is sometimes observed 

 in syphilitic arteritis obliterans (Plates XXIII. and XXIV., 

 Figs. 4 and 5). As may be seen on reference to Fig. 4, the 

 thickening is very irregular, and in consequence the lumen of 

 the vessel is unequally narrowed. This condition very closely 

 resembles not only arteritis obliterans as seen in syphilis, but 

 also in stonemason's phthisis, chronic tubercular phthisis, in 

 healing wounds, interstitial nephritis, and the like. In all 

 these processes, there is eventually a cutting off of the blood 

 supply from tissues which were originally supplied by the 

 arteries. It appears as though an exactly similar process is 

 here taking place. In the section under examination numer- 

 ous transverse (Fig. 4) and longitudinal sections of vessels 



