PANCREAS. 



89 



finely granular. These globules are of various 

 shapes, according as they are isolated or com- 



Fig. 60. 



Appearance of homogeneous globules of various sizes 

 and shapes, occasionally seen in the follicle of the 

 pancreas. From the Rat. {Magnified 200 dia- 

 meters.') 



pressed by neighbouring ones. They range in 

 size from ^-^ to ^i. o f an inch, and are evi- 

 dently not contained in any cell-membrane. 

 (Seejfg. 60.) The appearance, in my opinion, 

 results from a spontaneous solution of the 

 epithelium in the follicles, and a separation of 

 the different elements of the secretion ; but 

 what are the particular circumstances that de- 

 termine it I do not know; the longer the 

 object is kept under the microscope, the more 

 marked is the appearance, and the larger the 

 globules, from their running one into the 

 other : it is possible that endosmosis may have 

 something to do with it, for I do not remember 

 ever to have seen the appearance in specimens 

 promptly examined immediately after death.* 

 7. Occasionally there is an appearance of a 

 central cavity in each follicle, the epithelium 

 lining it in a single columnar-looking layer, 

 and leaving a central space unoccupied. The 

 central space thus left is very small, not ex- 

 ceeding in diameter that of the thickness of 

 the epithelial layer lining the follicle; it is 

 only now and then that this appearance can 

 be detected, and even then it requires careful 

 focussing to see it satisfactorily : it may either 

 arise from the epithelium being shed in suc- 

 cessive generations of layers, one passing 

 from the follicle as the succeeding crop is 

 produced, or it may be explained by the mere 

 liquefaction of the central and older cells, 

 which, escaping in a fluid form from the fol- 

 licle, leave the peripheral cells with a definite 



* Since writing the above, I have had satisfac- 

 tory evidence that the appearance is owing to en- 

 dosmosis. I have seen the globules form under the 

 microscope from their first trace to their attainment 

 of a size equal to that shown in the figure. Some- 

 times the endosmotic current is so strong as to 

 cause visible movement in the contents of the 

 follicles ; the globules are the endosmosed fluid, the 

 intervening material the granular contents of the 

 follicle ; in fact, the secretion. I have thought it 

 worth while to retain the figure and description, as 

 it is an appearance that might very easily give rise 

 to error. 



and even surface. At any rate, it is a rare 

 thing to see the appearance clearly, and when 

 it is visible, it requires accurate focussing for 

 its satisfactory display ; for if either the 

 nearer or more distant surface of the follicle 

 is in focus instead of the centre, all appear- 

 ance of cavity vanishes, and the follicle seems 

 to be full of epithelium. Perhaps it is in 

 part owing to this, and in part to the fact 

 that the condition accompanies a particular 

 and transitory stage of the secretion, that it is 



Fig. 61. 



A group of follicles from the pancreas of a Rat, 

 viewed so as to bring their central cavity into focus. 

 (Magnified 150 diameters.') 



not more frequently visible. I have repre- 

 sented it mfig. 61., as seen in a group of fol- 

 licles from the pancreas of a rat : it displays 

 the proportional thickness of the central ca- 

 vity and the epithelial lining, and shows one 

 or two follicles, where, from being out of 

 focus, the cavity is not visible and the follicle 

 appears solid throughout. It was sketched 

 immediately after death. 



Duct. The duct of the pancreas, like that 

 of other conglomerate glands, consists of three 

 coats : a middle, elastic, dense, fibrous, and 

 white ; an external, loose, and areolar ; and an 

 internal epithelial. Between the middle and 

 internal there is probably a basement mem- 

 brane, described, indeed, by some authors, but 

 which I have been unable to detect. 



The middle coat consists of a firm, dense, 

 and matted stratum of fibrous tissue, mainly 

 longitudinal in direction, but closely inter- 

 woven and netted together, very much re- 

 sembling white fibrous tissue in appearance, 

 but evidently not consisting of this entirely, 

 as the striation is not removed by acetic acid. 

 A certain amount of clarification, however, 

 is produced by adding the acid, and the fibres 

 that remain visible afterwards appear to con- 

 sist of a particular form of yellow fibrous 

 tissue, extremely fine, so as to lose the cha- 

 racteristic appearance of double outline and 

 even calibre. These fibres are exclusively 

 longitudinal and parallel, except towards the 

 outer surface of the duct where they inter- 

 lace. Besides these, acetic acid displays, 

 irregularly and sparingly scattered, some trans- 

 verse and some longitudinal, the nuclei of 

 some unstriped muscular fibres. These fibres 

 I have never been able to isolate or see satis- 

 factorily, for the density and opacity of 

 the fibrous tissue previous to the addition of 

 acetic acid renders them invisible : they lie 

 near the inner surface, and, from the paucity 

 of the nuclei, must be very few. 



The external coat is merely the loose 

 areolar web which connects the duct to the 



