THE THYMUS. 189 



are all seen terminating in loops close upon it. Besides these 

 blood-vessels a small quantity of connective tissue also appears 

 to enter into the formation of the thick walls of the glandular 

 lobes ; at all events, in their innermost portions, where the 

 larger vessels are situated, we find, often with tolerable distinct- 

 ness, a membrane supporting them, analogous to that lining the 

 central cavity. In other cases, however, and especially in 

 animals, an internal limitary membrane of this kind cannot be 

 demonstrated and the cavities of the lobules are bounded 

 immediately by the granular substance connecting the vessels, 

 between which, only some delicate indications of fibres are 

 apparent. In no case does there exist any epithelium lining 

 the cavities and consequently, the comparison of the innermost 

 part of their wall with a mucous membrane is untenable. 



The common cavity or central canal of the thymus, presents 

 the same structure as the lobules, except that externally there 

 is a thicker fibrous layer and internally, a less thick granular 

 stratum, with rather larger vessels. In a fully developed thymus 

 it, as well as all the secondary cavities, contains a greyish-white 

 or milky, faintly acid fluid, often in large quantity, in which, 

 together with a clear fluid abounding in albumen, numerous 

 nuclei, isolated cells and, under certain circumstances, also 

 concentrical corpuscles [vide infra) are contained. The lympha- 

 tics of the thymus are numerous and nerves may be readily 

 demonstrated upon the arteries, although they cannot be traced 

 as far as their terminations. 



[Besides the above-described normal elements, there occur, 

 especially at the period of involution of the organ, other peculiar 

 spherical structures, which, with Ecker, I would term the 

 concentric corpuscles of the thymus. They present very various 

 forms, which, however, it seems to me may conveniently be 

 reduced to two; viz. 1. simple, 0006 — O'Ol'" in size, with a 

 thick concentrically striated membrane and a granular sub- 

 stance in the interior, sometimes appearing like a nucleus, 

 sometimes as a cell; and 2. compound, as much as O'O^" or 

 even 0'08'" in size, and consisting of several simple corpuscles, 

 surrounded by a common laminated envelope. These bodies, 

 which were first noticed by Hassall and Virchow, and were 

 further investigated by Ecker and Bruch, it appears to me arise 



