562 EEPORT— 1882. 



in proportion as tlieir evolution is carried farther ; and thus is produced a paren- 

 chyma or solid organ. 



10. The capillary hlood-vessels are for the most part much more minute than 

 the smallest branches of the ducts of secreting canals and their cpecal extremities, 

 even in the most complex glandular organs. The elementary parts of glands, though 

 minute, are of such a size that the capillary blood-vessels form around them a net- 

 work which invests them. 



11. The formation of the glands in the embryo displays the same progressive 

 evolution from the simple to the complex state as is observed in ascending the 

 animal scale. The most perfect and complex glands of the higher animals, when 

 they first appear in the embryo of these animals, consist merely of the free efferent 

 ducts without any branches, and in that state exactly resemble the secreting 

 oi-gans of the lower animals. The glands are formed from the unbranched tubes 

 by a kind of efflorescence or ramification. 



12. The mode in which the extent of internal secreting surface of a gland is 

 realised is very various ; and no one kind of conformation is peculiar to any kind 

 of gland. Perfectly different glands ma}^ have a similar elementary structure, as 

 is the case, for instance, with the testes and the cortical substance of the kidneys. 

 And similar glands have often a perfectly different structure in different animals ; 

 of which the lachrymal glands, examined in the chelonia, birds, and mammalia, 

 afford an example. 



Johannes Miiller recognised thoroughly, as we have seen, that the character of 

 a secretion cannot be deduced from the structure of the organ which produces it. 

 Was he able to throw any light upon the mystery which had baffled all his pre- 

 decessors and to explain the cause of the specific endowments of the different 

 glandular organs ? Let us allow Miiller to speak : — 



'The peculiarity of secretions does not depend on .the internal conformation of 

 the glands; for, as I have sufficiently demonstrated, each 'secretion is in different 

 animals the product of the most various glandular structures, and very different 

 fluids are secreted by glands of similar organisation. The nature of the secretion 

 depends therefore solely on the peculiar vital properties of the organic substance 

 which firms the secreting canals, and which may remain the same, however 

 different the conformation of the secreting cavities may be ; while it may vary 

 extremely although the form of the canal or ducts remains the same.' It was the 

 living lining substance of the gland which, according to Johannes Miiller, formed 

 the secretion, at the expense of materials which it obtained fiom the blood of con- 

 tiguous capillaries. This living substance lining the inner recesses of the glands 

 had not yet been differentiated into its constituent units, the secreting cells, and 

 • therefore Miiller's statement wanted a certain detiniteness, though, so far as he 

 went, he was perfectly accurate. 



The Researches of John Goodsir. 



The success with which that eminent pupil of Johannes Miiller, Theodore 

 Schwann, had extended the generalisations of Schleiden (on the part taken by the 

 cell in the formation of vegetable structures) to the elucidation of the animal tissues, 

 had given the greatest impulse to the stud)' of animal histology, and a large number 

 of observers, especially in Germany and England, were directing their attention to 

 the discovery and studj^, in all tissues and organs, of the all-important cells. 



Purkinje had announced the hypothesis that the nucleated epithelium which he 

 discovered to line the gland-ducts might exercise secreting functions. Henle had 

 described with great minuteness the epithelium cells which line the ducts of the 

 principal glands and follicles, and which form the most superficial structures of 

 mucous membrane, and Schwann had suggested that this epithelium probably 

 played a part in the act of secretion. It was, however, unquestionably the Scottish 

 anatomist, John Goodsir, to whom was reserved the merit of establishing in an 

 indisputable manner the fact that the essential and ultimate secreting structures 

 in glands are the morphological units, the gland-cells. As Johannes Miiller had 

 examined the arrangements and coarser structure of glands throughout the animal 



