140 TUBERCLE. 



readily in detached slireds of the membrane, as in those vessels 

 which are still intact. In the latter case, they appear as staff- 

 shaped structures, embedded between the external contour of the 

 vessel and its muscular layer. These nuclei are not naked ; they 

 are surrounded by a small quantity of a finely-granular sub- 

 stance, which is chiefly heaped up in the direction of the long 

 axis of the vessel. A second contour, which surrounds the nuclei 

 at a variable distance, may be rendered visible, according to 

 //is, by the silvering process ; this would give the membrane 

 the sio-nificance of a lymphatic endothelial tube, though all 

 attempts to arrive at some reliable knowledge concerning its 

 relations to the lymphatic system have hitherto failed. This 

 membrane is the starting-point of the morbid growth, and that 

 too in its capacity as a lymphatic endothelium. The first stage 

 of the process consists in a marked augmentation of the residual 

 ]3rotoplasm which surrounds the nuclei. A fissiparous multipli- 

 cation of the nuclei coincides with it in point of time (fig. 43, 5). 

 The nuclei recede from one another ; and while some of them 

 may undergo repeated fission, others enter upon a peculiar 

 change. They assume more of a globular shape in place of their 

 former flattened, discoidal aspect ; as a result of this, they become 

 smaller in size ; whereas they were pale and finely granular, they 

 now assume a homogeneous lustre ; in a word they put on the 

 appearance which has already been referred to as characteristic 

 of the nuclei of the tubercle-cells ; at the same time, alterations 

 set in immediately around tlie nucleus. The protoplasm begins 

 to refract light more highly ; its density increases, so that the 

 nucleus looks as if it were surrounded by a spherical envelope of 

 ground glass ; the sphere is bounded by a line, indistinct at 

 first, but which subsequently becomes sharper and more definite ; 

 this limits the entire structure, and completes the tubercle-cell in 

 all essential respects. Fig. 43, 6, represents shreds of the adven- 

 tltia torn from the growing border of a small tubercle ; in the 

 layer of condensed protoplasm we see on the one hand complete 

 elements with others in process of development, and on the 

 other, cavities which correspond to those elements in form and 

 size ; the cells having dropped out during the mounting of the 

 specimen. Fig. 43, 7, shows the edge of a small vessel in 

 whose adventitia several tubercle-cells and mif^lei are em- 

 bedded. 



