88 



PANCREAS. 



mate structure of glands, has contributed 

 more than any other author to our knowledge 

 of this particular section of general anatomy. 

 In the human pancreas the follicles are so 

 closely packed that their individual shape 

 cannot well be seen ; but in the rodents the 

 arborescent arrangement of the gland exhibits 

 them well ; and they arc seen, when isolated, 

 to be ovoidal or nearly spherical*, although, 

 in the central part of the lobule, they become 

 variously polygonal from mutual compression. 

 The outline, however, even where they are 

 not compressed, is not that of smooth sphe- 

 rules, but presents slight convexities cor- 

 responding to the epithelium within them ; 

 but the endosmosis of water, by detaching 

 the epithelium from the basement membrane, 

 and at the same time distending the follicle, 

 causes these convexities to disappear. There 

 is great difference in the size of the follicles, 

 some being as much as j-g-g-th of an inch in 

 diameter, some as small as ^ji-g-th ; and the 

 extremes in size will often be contiguous, a 

 very small one packed among many large. 

 The average size of a pancreatic follicle is 

 about Tj^o-th of an inch. The number of fol- 

 licles in a single group varies still more, being 

 from half a dozen to a hundred or even more. 

 In the rodents these groups are often entirely 

 separate from one another on every side ; but 

 in most of the mammalia their isolation is not 

 so complete, and they are more or less 

 massed and fused together. 



Fig. 58. 



loose and unattached appearance, the simi- 

 larity of their granular contents to that of the 

 secretion when free, and the want of definite- 

 ness of outline in many of them, which seem 

 dissolving in their own contents, the cell-wall 

 having disappeared, and the cluster of con- 

 tained granules merely marking its situation. 

 (See Jig. 57.) In neither of the stages can I 

 detect nuclei. From the great opacity of the 

 more advanced cells, and their grouping 

 towards the centre of the follicle, they give a 

 portion of pancreas, viewed with a low power, 

 a mottled appearance, a dark spot marking 

 the centre of each follicle, and the number of 

 dark spots showing the number of follicles, 

 which, in some parts, from their close packing, 

 could not be otherwise counted 



When the follicles are ruptured, the epi- 

 thelium escapes, and the two forms may be 

 seen floating freely about. Fig. 58. repre- 

 sents some of the more advanced cells ; they 

 are magnified 400 diameters, and are seen to 

 be filled with the particular granular matter 

 which imparts to them their darkness and 

 opacity, and which differs only from the free 

 granular matter floating about in the secretion 

 in being localized and confined by the vesicular 

 envelope of the cell. What might be called 

 the granular or molecular base of the pan- 

 creatic fluid, is evidently the contents of these 

 mature cells, liberated by the rupture or solu- 

 tion of the cell-wall. 



The cells that have attained this appear- 

 ance, although they may be grouped together, 

 as seen in fig., 57. are never adherent to one 

 another. The less advanced cells, however 



Fig. 59. 



Isolated cells of mature secreting epithelium from the 

 pancreas of the Rat, showing their opaque granular 

 contents. (Magnified 400 diameters.) 



$. The epithelium is of the glandular type, 

 spheroidal or polygonal in shape, varying in 

 diameter from T^^th to -Tnn>th of an inch, 

 and presenting two distinct appearances, in- 

 dicating, I think, two stages of development 

 an early stage, and one of more complete 

 maturity. The cells of the early stage are 

 smaller, more spherical, homogeneous in 

 structure, and most abundant at the peri- 

 pherae of the follicles or in immediate contact 

 with the basement membrane. The more 

 advanced cells are larger, of more varied 

 shape, full of granular contents, and loosely 

 aggregated towards the centre of each follicle. 

 I consider the form first described to be the 

 early stage because the cells are so small, are 

 in contact with or near the cell-generating 

 surface, and are free from secretion con- 

 tents. The others, I imagine to be the more 

 advanced stage, from their greater size, their 



* In Cruveilhier's Anatomy, p. 533. note, it is said 

 that the ultimate follicles of the pancreas are 

 cylindrical, while those of the salivary glands are 

 slightly dilated. ( ?) 



Epithelium liberated by rupture of the follicles, show- 

 ing the method of detachment, and the mutual lateral 

 adhesion, of the cells. From the Mouse. (Mag- 

 nified 200 diameters.) 



or those in contact with the membrane of the 

 follicle, are often so closely adherent, that 

 when they escape from their containing fol- 

 licle they form little crescentic masses, as 

 seen in fig. 59., the convexity coinciding with 

 the follicle-membrane, the concavity with the 

 central space, and the adherent surfaces of 

 the cells presenting the appearance of radiat- 

 ing lines, passing from convexity to concavity 

 at right angles to them : this close package of 

 the epithelium gives it a columnar appearance ; 

 and, indeed, some of the little crescentic 

 groups referred to closely resemble the scraps 

 of sheaths of columnar epithelium shed from 

 an intestinal villus during digestion. 



Sometimes, instead of the follicles being 

 filled with distinct epithelium cells, they ap- 

 pear to contain a number of variously-sized 

 globules, of a smooth, homogeneous, and highly 

 refracting appearance, surrounded by a me- 

 dium of much less refracting power, and 



