THE THYMUS. 



591 



(injections, inflation). I believe that Simon is correct, when he asserts 

 that in such a (.lelicatc structure as the tJi?/mus, injection or inflation, 

 unless efl'ectcd with the greatest care, necessarily leads to error, and I am 

 also satisfied, that many of the observed " reservoirs" in the thi/mus 

 are only artificially produced ; but, nevertheless, I am of opinion, that 

 there really are thymus glands, containing, in "life, a central cavity 

 because I have seen such cavities extending through the entire thi/mus 

 or only through separate segments of it, and this in cases Avhere no pre- 

 paration of any kind or injection had been used. I look upon the oc- 

 currence of a narrow central canal, as the original and usual condition, 

 but believe, that in certain cases it may be expanded by a more abun- 

 dant formation of the secretion, and ultimately be converted into a large 

 cavity. 



§ 183. Intimate structure of tlie thymus. — "When a lobule is stripped 

 of its investing coat, consisting of common connective tissue, with fine 

 elastic fibres of the finer sort and fre- 

 quently with scattered fat-cells, its ex- Pi^ 244 

 ternal surface, fissured in correspon- 

 dence with the separate gland-granules, 



comes into view. Under stroncj mag- 



nifjnng powers, there is now presented 

 a very thin (0-0005-0-001 of a line), 

 indistinctly fibrous, or almost homo- 

 geneous membrane, quite correctly de- 

 scribed by Simon, which is continuous 

 over an entire lobule or even the whole 

 gland, and must be placed in the same 

 category with the wall of the follicles 

 in Peyer's patches, the tonsils, &c. 

 Within this envelop, between it and 

 the cavity of the lobule, lies a grayish- 

 white, soft, easily lacerable substance, 

 ^-J of a line thick, which, when ex- 

 amined microscopically, appears to consist of nothing but free nuclei 

 and minute cells, and on this account has, by agreement of all obser- 

 vers, hitherto been regarded as the secretion of the supposed gland- 

 vesicles. But this substance cannot be washed away, which would have 

 been the case had it lain loosely in the space enclosed by the delicate 

 membrane ; on the contrary, it exhibits a considerable degree of tough- 

 ness and resistance. AVhen examined more closely, it is, by degrees, 



Fig. 244. — Transverse section tliroujih the summit of an injected lobule of the thymus in 

 a Child, magnified SOdiarn.: a, membrane of the lobule ; 6, membrane of the gland-granules; 

 c, cavity of the lobule from which the larger vessels branch out into the granules, on the 

 surface of which they terminate, occasionally forming loops. 



