PANCREAS. 



87 



given by the most trustworthy authorities, all 

 conspire to invest the practical investigation 

 of the subject with an amount of difficulty 

 and doubt greater, I think, than that which 

 would beset almost any other path of micro- 

 scopical research. And I may add to this, 

 what would naturally be its accompaniment, 

 a deficiency on the part of the authors that I 

 have consulted, in that very kind of informa- 

 tion that the practical difficulties of original 

 research make one crave in others. The 

 only observations on which I think reliance is 

 to be placed for the solution of the difficulties 

 that the examination of a structure so in- 

 volved and delicate as the one under consi- 

 deration presents, are observations made with 

 the microscope on the parts, fresh, in situ, 

 unaffected by re-agents, and undisturbed by 

 such manipulation as shall interfere with the 

 normal relations of their minute anatomy; 

 and such observations I cannot find. Miiller's 

 descriptions and drawings on this subject, in 

 his admirable monograph, " De Glandularum 

 Secernentium Structura Penitiori," are either 

 taken from the parts unmagnified, or magnified 

 with such low powers as make them valueless 

 for the solution of the special difficulties of 

 the case. The same observation applies to the 

 accounts of the minute structure of the pan- 

 creas contained in the ordinary works on de- 

 scriptive anatomy, from their being descrip- 

 tions of the minute structure as seen by the 

 naked eye, or as made out by a coarse kind 

 of disintegration, or by mercurial injections. 



The most satisfactory microscopical ex- 

 aminations of the pancreas may be made, I 

 think, from those of the Rodents; for in them 

 the gland being spread out in its proper me- 

 sentery in an arborescent or seaweed-like 

 form, it is in some parts so thin as to trans- 

 mit sufficient light for its examination without 

 any compression or dissection whatever ; in- 

 deed, along the edges and in some of the 

 smallest lobules, the ultimate follicles are dis- 

 tributed in a single layer only. This arrange- 

 ment makes a careful and satisfactory scrutiny 

 much easier ; and I shall, therefore, in this 

 part of my paper, draw principally from the 

 appearances of the gland in these animals, as 

 the rat, rabbit, mouse ; at the same time the 

 close approximation in ultimate structure to 

 the human pancreas will make my observa- 

 tions apply as well to the gland in man as in 

 these lower mammalia. 



On putting a minute lobule of the pancreas 

 of a rat or mouse under the microscope, we 

 see a number of follicles grouped together, of 

 various forms and sizes, constituting, by their 

 grouping, the acini of the gland, or ultimate 

 granules visible to the naked eye ; and when 

 the acinus is constituted by a small number of 

 follicles, and isolated, the whole of it may be 

 brought under the field of the microscope at 

 once (as in fig. 57.). These follicles are 

 formed by the involution of the limitary mem- 

 brane of the gland, and they contain the se- 

 creting epithelium, and within that (at least 

 under some circumstances) a central cavity. 

 These elements of the follicle the basement 



membrane, the epithelium, and the cavity I 



shall consider in succession. 



Fig. 57. 



Minute lobule or acinus of the pancreas of a Mouse, 

 showing the two forms or stages of tlie epithelium, 

 and the varied forms and sizes of the. ultimate fol- 

 licles (magnified 180 diameters). 



a. The basement or limitary membrane. It 

 is to the modification and arrangement of this 

 fundamental tissue that the pancreas (in 

 common with all other glands, either folli- 

 cular or tubular, simple or compound) owes 

 its shape and appearance as a conglomerate 

 gland, and its position in the gland series as 

 a " compound gland with canals of the ramified 

 type having follicular extremities."* From 

 this membrane, as from a starting-point, the 

 distribution and anatomy of all the other ele- 

 ments of the gland structure proceed. The 

 branched character of the ducts, the parti- 

 cular manner- in which the follicles are 

 grouped, the racemose or panniculated cha- 

 racter of their clusters, the isolation of the 

 epithelium within them, the amount and ar- 

 rangement of the areolar tissue without them, 

 and the form of the capillary network, all 

 result from the particular way in which this 

 basement membrane is laid down. To this 

 simple truth anatomists have been a long time 

 in coming. Malpighi first, in 1665, an- 

 nounced the fact that the compound glands 

 were mere multiplications or repetitions of 

 the simple ones, and that all glands consisted 

 of tubes with blind dilated or undilated extre- 

 mities, which received the secretion from the 

 blood and poured it into the excretory duct 

 This view, after having some doubt thrown 

 upon it by the researches of Ruysch and the 

 experiments of Haller, has been entirely con- 

 firmed and greatly elaborated by the labours 

 of Muller, who, in his great work on the inti- 



* Mttller, Physiol. by Baly, vol. i. p. 444. 



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