A7i^. 20, 1874] 



JVA TURE 



329 



papilla; of the frog, and by Schwalbe and Loven in the gustatory 

 cells of the circumvallate and of some of the fungiform papils; in 

 men and animals. On the protected sides of the circumvallate 

 papilla; a peculiarity in the shape and arrangement of the epithe- 

 lial cells produces a series of taste-cones, the central cells of 

 which are furnished with hair-like prolongations similar to those 

 of the olfactory cells. 



In the otolith sacs and the ampulL-e of the semicircular canals 

 of the ear, llie nerve-filaments, having lost their white substance, 

 become connected with peculiar auditory cells and end in hair- 

 like processes between the epithelial cells. In the cochlea, too, 

 notwithstanding the complication of the examination produced 

 by the rods of Corti, there is reason to believe thnt the cells sup- 

 porting hairs which project beyond the epithelial surface are 

 connected with the primitive nerve-fibrils of the plexus below. 



Of the recorded instances in which nerves pass through base- 

 ment membranes to get into direct contact or continuity with the 

 superjacent epithelial cells, none is so striking as that of the 

 .salivary and other glands, if there be the least ground for the 

 remarkably detailed observations an^l suggestions of Plliiger. 

 They are of so much importance and interest in connection with 

 the whole process of secretion, that I ofl'er no excuse for directing 

 your attention to them, even though it may be proved that the 

 act of secretion is not attended with such marvellous and exten- 

 sive changes of structure as Pfliiger supposes. Up to a certain 

 point his observations may be easily and abundantly confirmed ; 

 beyond that there is much greater difficulty ; but this meeting 

 offers one of the most favouiable opportunities for extending our 

 knowledge by bringing diflerent observers into easy communica- 

 tion with each other, and enabling eacli to help the rest by stating 

 the means by which he had overcome what seemed at first to be 

 insuperable difficulties in the progress of an investigation. 



PlUiger calls attention to the very variable characters of the 

 alveoli, the secreting cells, and the excretory ducts of the salivary 

 glands. These parts, which were believed to have very deter- 

 minate sizes and characters, he declares to differ very greatly in 

 different parts of the same gland. The alveoli, occupied by what 

 we understan<l as secreting or glandular epithelial cells, and the 

 excretory ducts, lined by columnar epithelium, he thinks he can 

 prove to be but different stages of development of the same 

 structures, produced on the ends of the myriad nervous fila- 

 ments supplied to these glands. 



On this view glandular epithelial cells must be regarded as 

 special organs of termination of nerve-fibrils, like the auditory 

 cells, touch-corpuscles, olfactory cells, muscular fibre-cells, 

 and the like ; the relation between such structures and 

 the nerves becoming so close that it may be difficult, per- 

 haps impossible, to define their respective limits. Plhiger 

 has figured the nuclei of the cells of the alveoli of the salivary 

 glands, the salivary cells, connected with a delicate fibre, 

 which often pierces the surface of the cell in contact with the mem- 

 I'yana pivpria, and gives the cell the appearance of being stalked. 

 This appearance has also been seen by Schluter, Otto Weber, 

 Gianuzzi, Boll, and KoUiker ; and indeed the appearance which 

 Pfliiger has figured may be seen by anyone who will take the 

 trouble to examine the salivary glands of the common cockroach 

 [h'lii/ia nih-ii/a/is). This process was shown to me by my friend 

 and pupil, Mr. Charles Workman ; and I have several prepa- 

 rations which show a similar process to that which Plliiger has 

 observed and figured ; but that it is as clearly connected with 

 the nucleus of the cell as he describes it I am not prepared to 

 affirm. Plliiger says it is hollow, and often discharges a large 

 quantity of tenacious material which cleatly proceeds from the 

 nucleus. 



In the interior of the gland there are ducts lined with a thick 

 but single Layer of columnar epithelium, the cells of which are 

 clear and nucleated near their free end, but furnished with a 

 large number of extremely fine varicose hairs at the end con- 

 nected with the mcinl'iana propria. This epithelium becomes 

 thicker as the ducts proceed towards their connection with the 

 alveoli ; and as transparent drops can be seen transuding from 

 the ends of the cells when saliva has been made to flow by 

 irritation of the gland, Pfliiger concludes that they are important 

 secretory organs. Such ducts frequently form loops, or bend 

 suddenly, or possess diverticula. The epithelium of the ducts, 

 which carry the secretion out of the gland, is of a different and 

 apparently less important kind. 



Pfliiger diiccts special attention to the great number of nerves 

 connected with the alveoli. He has identified them in fresh 

 Specimens by their investment hire and there by an ordinary 



double-contoured medulla, by their being blackened byperosmic 

 acid, by their varicosities, and by tracing them to large and more 

 easily recognisable nerves. He finds them branching in great 

 numbers amongst the cells of the alveoli, and traces their fibrils 

 to the nuclei of the cells, sometimes after they have been con- 

 nected with multipolar ganglion-cells. Or nerves covered by 

 medulla and sheath, and containing numerous varicose a.xis 

 cylinders, branch, enlarge, and become covered with protoplasm 

 set with nuclei, forming what Pfliiger calls a protoplasmic foot, 

 and supposes to be a structure intermediate in character between 

 nervous and glandular tissue. And on the surface of the ducts 

 lined by columnar epithelium a nerve divides into a pencil-like 

 tuft of varicose fibrils, each of which Pfliiger says is directly con- 

 tinuous with one of the processes of a columnar epithelial cell. 

 I have frequently seen the pencil-like tuft of varicose fibrils on 

 the surface of the ducts lined by columnar epithelium ; but it is 

 not so easy to be sure that the fibrils are connected with the pro- 

 cesses of the cells. However, the statement is made in the most 

 positive way by Ffliiger, who has made these glands the subjects 

 of very special and lengthened investigation ; and his drawings 

 afford very strong corroborative testimony of the value of his 

 statements. Moreover, in independent observations on tlie pan- 

 creas, he has also traced the nerves to endings in the secreting 

 cells. 



But Pfliiger has gone greatly further than this. He has figured 

 the hair-like processes at the attached end of the columnar cells 

 in all stages of transition into salivary cells of new alveoli ; and 

 having previously found the nerves connected by varicose fibrils 

 with protoplasmic masses set with nuclei, he concludes that it is 

 possible that the salivary cells are developed on the ends of the 

 nerves without interference of their own nuclei, and that, as a 

 continual new formation of alveoli and salivary cells implies the 

 atrophy and disintegration of corresponding older parts, the 

 alveoli with pale offshoots of various forms which he has seen in 

 moles are evidences of such atrophy. 



With these numerous instances in which nerves are alleged to 

 pass through membranes to be connected with the cells on their 

 surfaces, as if these were their special modes of termination, we 

 might well be content until there has been time for further inves- 

 tigation by independent obseivers. But there are yet other in- 

 stances. Langeihans described, in 1868, a fine network of fibres in 

 the skin, from the superficial part of which fine non-medullated 

 fibres pass out of the cutis and end in the Malpighian layer of the 

 epidermis. He siw in the epidermis a'so well-marked cells 

 which gave off several processes towards the horny layer, and 

 one long slender process which passed through the Malpighian 

 layer into the cutis. He considers these cells to be nervous, and 

 their peripheral processes to be the terminal parts of the nerves 

 of the skin. C. J. Eberth agrees in the main with Langerhans, 

 and recognises fine nerve-fibres passing from the nerves of the 

 cutis into the deeper layer of cuticiilar cells, and also star-and- 

 spindle-shaped cells in the cuticle, which he suggests may be 

 nervous structures, though he has not traced them in connection 

 with nerve-fibres. 



On the surface of young fishes and Amphibia F. E. Schutze 

 has described nerve-hairs arranged in the form of tufts or brushes 

 very much as in the case in the organ of hearing ; in this in- 

 stance the brush-like endings of the nerves are probably con- 

 nected with touch. 



Cohnheim has described the corneal nerves as forming a super- 

 ficial plexus under the anterior elastic lamina ; from this per- 

 forating branches pass perpendicularly through the lamina, and 

 then under the epithelium, break up into brush-like or star- 

 shaped finer branches, which form a plexus giving off fine nerves 

 at tolerably regular intervals between the deep column.ar cells 

 and the more superficial spheroidal ones, and dividing at length 

 into their finest branches, which end by somewhat swollen ex- 

 tremities in the most superficial epithelial layers. Thus the 

 exquisite sensibility of the front of the eye, like that of the 

 olfactory or gustatory mucous membranes, may be accounted for. 



When I look upon the vast amount of research which has been 

 applied to this department of I'iology for some years past, and 

 think that the instrument which has afforded the great means for 

 it was only perfected so as to be capable of use for such purposes 

 about 1820, X cannot but congratulate the Section on the abun- 

 dant fruits we are reaping. 



And when, in addition, I contemplate the amount of certainty 

 which physical science has imputed to physiology by furnishing 

 the means of examining and accurately measuring the rates of 

 transmission of rene-cunents, of obtaining liacings of the respi- 



