502 



MUCOUS MEMBRANE. 



tinuous with that of the duct. Such observa- 

 tions seem to me in a great measure conclusive 

 on this subject ; and 1 am strengthened in this 

 view by the fact, that the capsules of the 

 Malpighian bodies of the kidney are now 

 universally considered to be perfectly closed 

 vesicles, whereas they are in reality the ex- 

 panded wall of the duct, as I have lately 

 shown by several kinds of proof.* But what- 

 ever may be the real fact in the matter under 

 dispute, it is admitted by all that the epithelium 

 is formed in enormous quantities, and is being 

 continually thrown off; which is the circum- 

 stance chiefly intended to be insisted on at 

 present. 



In the healthy bile also, in the urine, and in 

 various other secretions Dr. Henle has met 

 with particles of epithelium detached from the 

 excretory passages, and in different stages of 

 decay. 



Turning to those two great emunctories, the 

 liver and kidneys, in the secretions of which 

 no trace of the epithelium of the secreting part 

 of the organs can be detected, we might be 

 disposed, on a slight consideration, to conclude 

 the evidence they furnish to be unfavourable to 

 the general position here advanced. We must, 

 indeed, be content for the present to acknow- 

 ledge that it is less plain and direct, and 

 shrouded in our great ignorance concerning the 

 play of chemical affinities in living bodies; 

 but still it is too interesting and important to 

 be passed over in silence. Though the epithe- 

 lium of these organs be not detached entire, as 

 in many other cases, there is much, in each 

 instance, to explain the discrepancy consistently 

 with the theory in question. 



1 have described the lobules of the liver as 

 consisting of a solid plexus of capillary blood- 

 vessels, in the meshes of which is a congeries 

 of epithelial particles. We possess no accurate 

 account of the mode of termination of the 

 biliary ducts ; but it seems clear, from the 

 small meshes of the vascular plexus being 

 completely filled by the epithelium, that no 

 true ducts, i. e. tubes, penetrate the substance 

 of the lobules: the tubular ducts probably 

 commence on the surface of the lobules. The 

 epithelium of the lobules is doubtless conti- 

 nuous with that of the ducts, but the cavity of 

 the ducts and their basement membrane termi- 

 nate at the surface of each lobule. Though the 

 cavity of the ducts be not continued within the 

 lobule, yet it is very possible that injection 

 urged along the ducts might insinuate itself by 

 the side of the epithelium into the interstices 

 of the vascular plexus, and thus, like the 

 epithelium itself, form a solid plexus within 

 the lobule. This appearance probably led Mr. 

 Kiernan to describe the termination of the ducts 

 as forming a plexus within the lobule, the 

 lobular biliary plexus. And this description 

 must be allowed to be essentially correct; for 

 although the cavity of the duct cease at the 

 surface, the epithelium of the lobule is, in 

 respect of function, its real continuation. I 

 have further observed, that although the epithe- 



Phil. Trans. 1842, Pi. I. p. 59. 



lium of the lobule has, on the whole, a plexf- 

 form arrangement, yet its particles in some 

 measure aflect a radiating direction from the 

 central axis towards the circumference, perhnps 

 towards certain parts only; and when a lobule 

 is broken up by violence, the resulting frag- 

 ments of epithelium are apt to consist of a 

 linear series of particles. Many of the particles, 

 too, are smaller than the rest, and have all the 

 appearance of having been recently formed and 

 as yet incompletely developed. It is also 

 remarkable that the particles should contain 

 granules of oily matter in their interior; for 

 although chemical analysis has detected diffe- 

 rences between this substance and cholesterine,* 

 yet as the chief peculiar principles of the bile 

 are forms of hydro-carbon, the coincidence 

 cannot be an accidental one. It is not con- 

 tended that the contents of these particles are 

 the finished secretion, but rather that their 

 chemical constitution undergoes some modifi- 

 cations during the disintegrating process. And 

 it is worthy of notice, that in many cases where 

 the decarbonizing function of the lungs is 

 slowly but greatly interfered with, as in phthisis 

 pulmonalis, and where the liver is consequently 

 called into increased activity as a compensating 

 organ, these oily globules exist in such abun- 

 dance and size as to gorge and swell the parti- 

 cles (and therefore the whole viscus) to nearly 

 double their natural bulk.f But this is not all 

 the evidence, that this epithelium is the source 

 of the bile. I am informed by my friend, Dr. 

 W. Budd, that Dr. Henle in his recent edition 

 of Soemmering, of which I have not yet been 

 able to obtain a copy, describes the epithelial 

 particles as appearing yellow or yellowish brown 

 in direct light, and as probably containing bile. 

 He also states that the presence of the fatty 

 globules in the epithelium is inconstant, and 

 corresponds with the varying fatty contents of 

 the bile. He is unable at present to determine 

 in what manner the contents of the particles 

 find their way into the ducts. 



The foregoing facts, taken together, afford a 

 very strong presumption that the epithelial 

 particles of the lobules are theagent assimilating 

 the secretion from the blood. It would be 

 still more satisfactory if particles could be found 

 undergoing decay. Meanwhile it seems im- 

 possible to assign to them any other office, if 

 it be granted that the sole function of the liver 

 is to secrete bile. For in the case of other 

 glands, the only other use that can with any 

 degree of plausibility be attributed to the epi- 

 thelium is that of its serving to defend the 

 secreting membrane from the contact of the 

 secretion, and to prevent the latter from re- 

 entering the blood. And it cannot exist for 

 that purpose in the liver, because it is itself 

 the only structure besides the bloodvessels, and 

 does not constitute a lining membrane. 



The peculiarity in the minute structure of 

 the kidneys, which bears on the present ques- 

 tion, is of a kind entirely different from any 

 presented by the liver, and yet tends to establish 

 a similar conclusion. It consists of a special 



* Kuehn, Kastner's Archiv. xiii. p. 337. 

 f A uthor in Lancet, Jan. 1842. 



