SECT. l82.] 



STRUCTURE OF THE THYMUS. 



397 



concur with Simon, to the extent of asserting that the injection, or 

 blowing-up of such a delicate structure as the thymus, must lead 

 to error, if not performed with the greatest precaution ; and I am 

 further convinced, that many of the so-called ' reservoirs' observed 

 in the thymus have been made artificially only. Nevertheless, I 

 am of opinion that thymus glands really occur which, during life, 

 contain a large central cavity, since I have seen such a cavity in 

 cases where no kind of preparation or injection was practised, and 

 here it has extended through the whole thymus, or only through 

 separate sections of it. I hold the occurrence of a narrow central 

 canal to be the normal and usual condition; but I believe that, in 

 certain cases, it may become dilated by a more abundant formation 

 of the secretion, and ultimately be converted into a large cavity. 



In a very meritorious work on the structure of the thymus, 

 Jendrassik has advanced the doctrine that it is originally made up 

 of isolated lobules, which only become conjoined subsequently and 

 in particular cases. But by an examination of the thymus of mam- 

 malia, especially of the calf, this view may be shown to be wholly 

 untenable; and the study of the development of the gland is also 

 fatal to such a supposition. Such investigations will demonstrate 

 readily and conclusively the exist- 

 ence of a single branching central 

 cavity, such as I have described (see ^ 



also my Micr. Anat., ii. 2, fig. 294). ^ 



§ 182. Intimate Structure of the 

 Thymus. — The connective tissue 

 which envelopes the thymus has the 

 same characters as elsewhere; it 

 contains fine elastic fibres, and fre- 

 quently interspersed fat-cells. If it 

 be removed from a lobule, the outer 

 surface, fissured between the indi- 

 vidual acini, comes to view. By 

 strong magnifying powers, there is 

 here seen a very thin membrane 

 (o - ooo5'" to o'ooi'" in thickness), 

 indistinctly striated or almost homo- 



Fig. 165. 



geneous, which has been well de- 

 scribed by Simon. This belongs to 

 an entire lobule, or even surrounds 

 the whole gland continuously, and is to be regarded in the same 



Transverse section through the apex of 

 an injected lobule of the thymus of a 

 child; magnified 30 times, a. Envelope 

 of the lobule. 6. Membrane of the acini. 

 c. Cavity of the lobule, from which the 

 large vessels ramify into the acini, and 

 partly terminate with loops upon the sur- 

 face of them. 



