The stalk consists, as has been said, of a production of the neurilem ma enclosing a single nerve-tube. It sometimes happens that there are two nerve-tubes, but then there are two corpuscles on the single stem, either in close apposition, or actually enveloped by a few cap sules common to both. The nerve-tube in the stalk is undulating, and being accompanied by white fibrous tissue is easily distinguished by its peculiar structure. The artery and vein supplying the corpuscle are also included in the stalk.
The channel which the stalk occupies in its passage through the capsules, is conical and comes to a termination at the proximal end of the innermost capsule. ' It is furnished with a membranous wall, with which the fibrous tissue of the stalk is united on the inside and the several capsules on the other, and by this means the intercapsular spaces are preserved closed, and their fluid retained. This wall usually presents irregularities of outline, and often a cellular ap ce, where the capsules, and especially t=er ones, join it. It is perfo rated by the minute vessels as they enter some of the intercapsular spaces (fig. 480 The capsules themselves are inelastic mem branes, analogous probably to the white fibrous tissue, and furnished with clear transparent nuclei that project chiefly on the inner surface. This is true of all the capsules, but in the outer system or those thicker and stronger ones be tween which fluid intervenes, there is evidence of a double wall ; for in addition to the clear double line whidi distinguishes all, these pre sent also on their outside, when seen edgeways, a series of dots, vvhich indicate a system of transverse or circular fibres, and in fact the corpuscle, when brought 'into focus, shows no other fibrillation than this transverse one. Al most all appearance of a fibrous texture is re moved by acetic acid, so that the yellow or elastic fibre does not appear to form any portion of the capsular membranes. The outermost capsule, indeed, is invested with both the elastic and the inelastic fibres, but these are to be regarded as belonging rather to the areolar tissue in which the corpuscles are imbedded, than to these organs themselves. The capsules are united together by the wall of the channel of the stalk. They are also joined here and there by partial membranous septa passing directly or obliquely across the intercapsular spaces, and which seem to be of the same na ture as the c-apsules themselves. Pacini de
scribes further a union of the capsules at the distal end in the axis of the corpuscle, which is denied by Henle and to exist. I have had, however, unequivocal evidence of its existence, especially between the inner capsules, when they have been artificially distended by water, although it often appears to cease to-. wards the surface. When the end of the cap sules is bent on itself, the line of this intercap sular union is less easy to trace.
The small artery supplying the corpuscle subdivides in the channel of the stalk into its three, four, or more capillaries, which pierce the wall and enter the intercapsular spaces. After advancing in these for a variable distance they form loops, and return by a similar route to the small corresponding vein. In the larger corpuscles I have seen a little bunch of vessels formed near the further end by some of these capillaries. In most cases a single capillary accompanies the nerve-tube as far as the central capsule, and then passes for some vray upon its wall, sometimes in a spiral direction. If a perfectly fresh corpuscle from the mesentery of a cat be examined before the blood has drained off, the addition of a little water will occa sionally induce a rapid movement of the con tents of these minute vessels under the eye of the observer, by gaining entrance to their interior; and few objects are more beautiful than the miniature circulation thus artificially brought about for a brief period. The capil laries have their proper walls, furnished with nuclei.
The central cavity, in size, and particularly in shape, is liable to much variety. It has been already stated to be not unfrequently bent upon itself towards the further end ; sometimes it is bifurcated, or, more correctly, branched, the offset then passing in a recurrent course either from the commencement or the middle part of its length. In this case the branch is surrounded by the same series of internal close capsules, and external ones separated by fluid, which encircle the principal cavity, only accom modated to the irregular conformation. How ever the central cavity is modified, it always retains its transparent character, and on its inner surface exhibits very faintly marked elongated nuclei, which most probably belong to the wall of the inner capsule.