TRANSACTIONS OF SECTION D. — DEFT. ANATOMY AND rHYSIOLOGY. 561 



the liver of larval salamanders, that, in glands, arteries never end in any other 

 mode than by capillaries leading into veins. lie set himself then to study in 

 the case of most glands, and in a large variety of animals, the relationship of 

 gland-ducts to the truly secreting parts of the orgau, and the relation of the blood- 

 vessels to these. Basing himself upon these anatomical studies of adult organs, 

 and upon a careful study of the development of glands — a study which had 

 been attempted slightly by Malpighi, and more satisfactorily in the case of the 

 parotid by E. II. Weber ' — Miiller came to the conclusion that all glands possessed 

 of a duct are only involutions more or less complex of membranes, the largest 

 number being involutions of the external investment of the body or of the mem- 

 branes opening upon its surface. The following are the general results relative to 

 the structure of glands which Miiller deduced from the anatomical study of indi- 

 vidual organs : — ^ 



1. However various the forms of their elementary parts, all secreting glands 

 without exception (not only those o£- the human body, but all met with in the 

 animal kingdom) follow the same law of conformation, and constitute an un- 

 interrupted series from the simplest follicle to the most complex gland. 



2. No line of demarcation can be drawn between the secreting organs of inver- 

 tebrata and those of vertebrate animals ; not merelj- do we meet with the simplest 

 sacs and tubular secreting organs, like those of insects, in the higher animals, but 

 there is a gradual transition from these simple secreting organs to the glands of the 

 most perfect vertebrata. 



3. All glands agree in affording bv their interior a large surface for secretion. 

 The varieties of internal surface by which the great end — extent of surface in a 

 small space — is attained, are very numerous. 



4. Acini, in the hypothetical sense in which the term has been used by 

 writers — in the sense, viz., of secreting granules — do not really exist ; there are no 

 glomeruli of blood-vessels with ducts arising from them in a mysterious way, as 

 has been supposed, whatever notions may have been held regarding them. 



5. The parts described as acini are merely masses formed by the agglomeration 

 of the extremities of the secreting canals ; frequently, indeed, they are formed of 

 minute vesicles aggregated together in grape-like bunches, which maj' be injected 

 with mercury, and are often susceptible of iuflation. 



6. In many glands which have been incorrectly described to have acini or 

 secreting gr.anules, there are not even the hollow vesicular acini; the secreting 

 tubes, instead of terminating in vesicles or cells, form long convoluted canals or 

 straight tubuli or short caeca. 



7. It has been demonstrated in the case of all glands that the blood-vessels are 

 not continuous with the secreting tubes — that the minute vessels bear the same 

 relation to the coats of the hollow secreting canals, and their closed extremities, 

 as to any other delicate secreting membrane, such as, for example, the mucous 

 membrane of pulmonary air-cells. 



8. The arborescent ramifications of the blood-%'essels accomp.any the ducts in 

 their development, and the reticulated capillaries in which the blood-vessels 

 terminate are extended over all the closed elementary parts of the gland and 

 supply them with blood. In the chick we may observe the sinuiltaneous de- 

 velopment of the two systems ; in proportion as the development of internal 

 surface from a plain membrane to crecuin and ramified coeca proceeds, the vas- 

 cular layer of the originally simple membrane is raised on the exterior of the 

 efflorescence. 



9. The ramified canals and tubes, which when the structure is simple, as in 

 insects and Crustacea, and even in some glands of the mammalia, lie free and 

 unconnected, become more aggregated together, and acquire a common covering, 



' E. H. Weber, Beohacldniiflcii iihcr die Sfructi(r einic/cr cnnf/lomcrirtcn und 

 clnfachen Drilsi'ii vii/l ihrc crxtc Eniiviclirlunri. Meckers Arc/tir for 1827, p. 274. 



'' This abstract of Miillcr's general conclusions has been abbreviated from the 

 sections treating on tliis subject in his £:/cmct/ts of Pliysivlof/i/. See Translation by 

 Dr. Baly, London, 1838, vol. i. p. 45G ct seq. 



18S2. 



