MUCOUS MEMBRANE. 



487 



Fig. 273. 



A portion of a tribute of the human 

 kidney, magnified 300 diameters. 



At , the basement membrane and 

 epithelium are both seen in a 

 natural state. At b, the base- 

 ment membrane has been sepa- 

 rated, and the epithelium is some- 

 what swollen, and its outline 

 woolly.' At c, the epithelium 

 has been detached and the base- 

 ment membrane is seen somewhat 

 wrinkled : d, a detached epithe- 

 lial particle seen in face ; its 

 minutely mottled texture is not 

 represented in the wood-cut. 



most probably the earlv condition of the new 

 or advancing series of these particles. Its 

 thickness in the kidney certainly does not ex- 

 ceed the sjffijgth of an English inch. I have dis- 

 covered, that in the Malpighian bodies of the 

 kidney, which are the dilated extremities of 

 the urmiferous ducts, with an enclosed tuft of 

 arterial capillaries, the basement membrane is 

 often, to some extent, naturally bare, i.e. without 

 a covering of epithelium. This is the only situa- 

 tion of the body in which such an arrangement 

 is known. 



In the testis, the same membrane may be 

 shewn without difficulty to be that which gives 

 to its secreting tubules their peculiar strength ; 

 and here, as might be expected, it is somewhat 

 modified. The difference is principally as 

 regards its thickness, which here reaches -n^th 

 of an English inch, and in some animals 



Fig. 274. 



appear to form an integrant part of the wall 

 of the canal. 



A portion of a tubule of the testis (Guinea-pig, Co- 

 baya) f magnified 300 diameters. 



a a, basement membrane ; a, corpuscle in its sub- 

 stance ; b b, epithelium in situ, consisting of par- 

 ticles of different dimensions, with minute gra- 

 nules in their interstices ; c, cavity of the tubule 

 full of detached epithelium particles, of various 

 size and appearance, and mingled with nume- 

 rous seminal animalcules ; d, one of these semi- 

 nal animalcules. 



even exceeds that amount, its essential charac- 

 ters, however, remaining the same. In the 

 larger tubes, emerging from the gland, this 

 tunic becomes gradually invested by a delicate 

 fibrous layer, by which the vascular network is 

 attached to it, and which at first sight may 



vesicles of the jiancn-us of the dot), magnified 

 300 diameters. 



The basement membrane is seen at a a a, where the 

 epithelium has been a little detached. 



In the salivary and all the allied glands, 

 the basement membrane admits of being easily 

 demonstrated. A very thin slice of the fresh 

 organ should be torn by needles, gently washed, 

 atid inspected under a high power. The termi- 

 nal vesicles of the duct will then be brought 

 into view and their outline seen to be perfectly 

 sharp and linear (fig. 275, a a a). In parts 

 where the epithelium which they contain has 

 been loosened, the basement membrane will be 

 left in relief. It is of extreme delicacy ; and, as 

 in all other situations, its capillary plexus (when 

 well filled with coloured material) may be seen 

 ramifying, not in its substance (for its tenuity 

 renders such a disposition impossible), but on 

 its parenchymal surface. 



I have sought in vain for the basement mem- 

 brane in the lobules of the liver, and I am in- 

 clined to think that it does not exist in this 

 gland, except in the excretory part of the bile 

 ducts. 



In the air-cells of the lungs the basement 

 membrane assumes a most interesting and re- 

 markable developement, for it constitutes almost 

 the entire thickness of their walls, the epithe- 

 lium being of extreme delicacy. It appears to 

 be here strengthened by interlacing arches of 

 elastic fibrous tissue, but to be itself transpa- 

 rent and homogeneous, as elsewhere. It is on 

 its parenchymal surface that the close vascular 

 web is spread out. (See PULMO.) 



But this membrane may be also detected in 

 every part of the alimentary tube, which is 

 more characteristically mucous, in that, viz. in- 

 tervening between the cardia and the lower ex- 

 tremity of the canal. Here it deserves an 

 attentive study on account of the apparent com- 

 plexity of its foldings, and because its exist- 

 ence here offers the most unequivocal proof 

 which we possess, of the anatomical identity of 

 the true glands with the membranes usually 

 called mucous. As it is more delicate in this 

 part than any other, and difficult of detection 

 by reason of the enormous preponderance of its 

 epithelial investment, I shall describe the man- 

 ner in which it may be best observed. The 

 specimen should be as fresh and healthy as 

 possible, or should have been immersed in 



