MUCOUS MEMBRANE. 



501 



festly the same structures, detached and matted 

 together. The secretion found in the tubules 

 of the testis is chiefly composed of epithelial 

 particles resembling those attached to the base- 

 ment membrane of the tubules. Some of these 

 are very perfect, others have undergone changes. 

 It has been already stated that the seminal ani- 

 malcules are most probably a developement of 

 some of these particles, not altogether different 

 in its nature from that of the cilia found upon 

 them in other situations. The secretion of an 

 ordinary mucous follicle is likewise made up 

 of epithelial particles resembling those still 

 attached to the membrane. The thick, semi- 

 fluid mucus found in the stomach has been 

 shown by Wasmann* to consist of rounded 

 nucleated particles, which both in size and 

 shape correspond with those of the stomach 

 tubules. This mucus may be even seen pro- 

 jecting from the cells into which these tubules 

 discharge themselves, and no doubt can exist 

 that the proper secretion of this organ is chiefly 

 composed of the bulky epithelium thrown off 

 by the tubules; a view corroborated by the 

 fact,f that this mucous membrane, consisting 

 almost solely of epithelium, when mixed with 

 certain acids naturally existing in the gastric 

 juice, evinces the same powers of dissolving 

 alimentary substances as that wonderful men- 

 struum itself. The same thing may be ob- 

 served in the intestinal canal, where the adhe- 

 sive mucus is little else than the aggregated 

 epithelial caps of the villi, together with that 

 which has escaped from the vertical tubes of 

 the membrane. These facts may be always 

 verified in a healthy animal just killed, and 

 may thus be shewn to be independent of any 

 morbid action. The legitimate conclusion from 

 them seems to be this : that the peculiar prin- 

 ciples of these respective secretions are lodged 

 in the epithelial particles ; having been depo- 

 sited there from the blood, in the natural 

 course of developement. In other words, the 

 process of secretion in these cases consists in 

 tm assimilation of the material from the blood 

 by an organized tissue, which, when fully de- 

 veloped, is loosened and shed. 



This view, so captivating by its simplicity, 

 has certainly much satisfactory evidence in its 

 favour, and it may, at least, be regarded as 

 sufficiently established to constitute a strong 

 presumption in favour of the general position, 

 that all secretion is primarily assimilation. 



That the epithelial particles, when their 

 growth is completed, should detach themselves 

 in a more or less entire state, in all cases, from 

 the membrane to which they have adhered, 

 cannot be supposed essential to this general 

 position, and even the total absence of any 

 vestiges of these particles from any particular 

 secretion would scarcely form a valid argument 

 against it. For at present we know of no reason 

 why the assimilated material should not be 

 gradually given up by a slow disintegration or 

 deliquescence of the particles, or even by a 



' De digestione nonnulla. Berol. 1839. 

 t Muller's Archiv. 1836, page 90. Schwann, 

 liber das Wesen dcs Verdanungs prozcsses. 



continual separation of it without a concomitant 

 destruction of the particles themselves. 



But in numerous instances besides those that 

 have been mentioned, there is more or less 

 direct evidence of an actual shedding and con- 

 tinual renovation of the epithelium. The scaly 

 variety of this tissue, whether on skin or mu- 

 cous membranes, is a wide-spread example of 

 this: the particles may be observed to augment 

 in size by the intus-susception of new material 

 from the blood, afterwards to undergo a slow 

 loss of substance, and, finally, to lose their 

 connection with the body altogether. They 

 retain their position till nothing but the nucleus 

 and cell-membrane remain, till they are re- 

 duced, as it were, to a mere skeleton. How 

 the material thus separated from the body is to 

 be distinguished from a secretion, it would not 

 be easy to decide. In the saliva of the mouth, 

 are present, not only detached scales, but globu- 

 lar nucleated particles, of a very delicate aspect 

 and regular character, which seem manifestly 

 to come from the salivary glands. They differ 

 in some respects from the epithelium of these 

 organs, but appear most probably to be par- 

 ticles of it altered by endosmose of the water 

 of the secretion through the cell-membrane ; 

 for the ultimate vesicles and ducts of these 

 glands are not merely lined, but filled, with 

 epithelial particles, which, being thrown off 

 from the basement membrane, must in due 

 time escape to make room for the advancing 

 series : and yet none of them in an unaltered 

 state are found in the saliva. 



I may in this place refer to an opinion 

 recently entertained in Germany, that the 

 secreting membrane of certain glands is arranged 

 in the form of closed vesicles filled with nu- 

 cleated particles, which, from time to time, 

 are discharged, as the secretion, by the bursting 

 of the cell in which they are contained. Henle* 

 conceives that this arrangement exists in the 

 mammary, salivary, and lachrymal glands, as 

 well as in almost every mucous membrane, 

 however apparently plain and simple. Was- 

 mannf has described a similar structure in the 

 middle part of the stomach of the pig. This 

 view of the existence of closed vesicles is 

 obviously at variance with the general view 

 before given of the universal continuity of the 

 simple membrane of the mucous system. I 

 am familiar with many of the appearances on 

 which it is founded, and without presuming to 

 pronounce them very decidedly deceptive, I 

 may state that hitherto my observations induce 

 me to agree with Dr. Baly J in his rejection of 

 the interpretation put upon them by the Ger- 

 man anatomists. A thin slice of a mass of the 

 many-lobed terminal vesicles of one of these 

 glands, especially if compressed, very readily 

 assumes the aspect of a congeries of cells, each 

 entirely surrounded by an envelope of base- 

 ment membrane. But I have several times, in 

 favourable sections, observed this membrane 

 passing off into a neck, and becoming con- 



Muller's Archiv. 1839, p. xlv. 



De digestione nonnulla. Berol. 1.839. 



Translation of Muller's Physiology, p. 



504^ 



