188 SPECIAL HISTOLOGY. 



exhibits a considerable degree of toughness and resistance. 

 When examined more closely, it is, by degrees, apparent that 

 other elements, to some extent of quite an unexpected kind, 

 enter into its composition; as for instance, blood-vessels, and also 

 a smaller quantity of afib?*ous substance of the nature of connec- 

 tive tissue, so that a structure not unlike that of the contents 

 of the Peyerian follicles is presented. 



Of the elements of the walls of the thymus-lobules, the 

 vesicular, together with a small quantity of a connecting fluid, 

 constitute the main bulk. Among these, free nuclei 0*002 — 

 0*005' /; in size, of a round slightly flattened shape, with homo- 

 geneous, clear contents, which become troubled and granular 

 in soda and acetic acid and with or without a nucleolus, are 

 always present in very great numbers. Secondly, as I 

 find, agreeing with Ecker but in opposition to Simon, cells also 

 are never wanting, though existing of very various sizes, from 

 0004'" to 0*01'", and, though varying in number as well, 

 still much less numerous than the nuclei. Their nuclei are 

 for the most part simple and distinct, and the contents pale or 

 with scattered fat- granules, or, and this Ecker says that he 

 has noticed after the complete development of the organ, they 

 are without nuclei and entirely filled with fat. In the midst of 

 these elements run numerous blood-vessels of larger and smaller 

 size. The main trunks running on the outer aspect and close 

 upon the central cavity in the longitudinal direction of the organ, 

 give off a large number of branches to the central cavity, which, 

 penetrating its walls, reach its internal surface, and there ramify 

 minutely in a delicate pellicle, composed of connective tissue, 

 with which it is lined, anastomosing and also forming tolerably 

 close capillary plexuses. From these arterial plexuses, at every 

 point where the lobules open, numerous vessels arise and enter 

 them, taking their course in the innermost portion of the 

 thick boundary wall, and then ramify towards the exterior in 

 the separate gland- granules, so as to constitute a capillary 

 plexus entirely filling them, composed of vessels 0*003 — 0*005'" 

 in diameter, and with meshes of 0*01 — 0*02"' (fig. 244). The 

 distribution of these vessels, in Man, is so limited to the interior 

 of the gland-granules, that, even when these have been most com- 

 pletely displayed, not a single vessel is found on the outer aspect 

 of their structureless investing membrane; on the contrary they 



