On the Changes in Serous Glands During Secretion
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ON THE CHANGES IN SEROUS GLANDS DURING SECRETION. By J. N. LANGLEY, M.A., Fellow of Trinity College, Cambridge. (Plates VII., VIII.) [From the Physiological Laboratory, Cambridge.] TIE examination of the changes in gland-cells during activity is usually made by hardening glands before and after activity and comparing the stained sections. This method affords much information about certain changes in chemical constitution, such as an increase or decrease in the amount of mucin; moreover certain morphological changes, especially those affecting the nuclei, can often only be made out by the use of reagents. Nevertheless inferences drawn from knowledge so gained are open to grave suspicion when not supported by observations made on the living tissue. We have one case in which glandular tissue has been directly observed during life at rest and in activity, viz. the pancreas1. Here the observations have in the main confirmed the conclusions already deduced from the study of the hardened gland'. The variations in the granular zone occurred alike in both cases. The following will, however, I think shew that the coincidence in the case of the pancreas is not a necessary one, and that with the salivary glands the examination of the living tissue makes a con- siderable modification in the views gathered from hardened specimens requisite. To obtain glands in the living condition for observation, I have either: Cut off the thin edge of a lobule with sharp scissors and at once mounted it: this is best adapted for thin or soft glands, such as the parotid of the rabbit. Or cut out a piece of the gland about the size of a pea, and made a thin section with a sharp razor or with a Valentin's knife; this serves fairly well for more consistent glands. Kiihne and Lea. Verhd. des Heidelb. natur-hist. Vereins. Ed. x. x. 3, 1876. HHeidenhain. Pfluger's rchiv. Bd. x. s. 557, 1875. 26-2 J. N. LANGLEY. In either case it is best to mount without adding any fluid, and to examine the more central parts of the specimen; the ordinary indifferent fluids may however be used; of these salt solution is, as far as my experience goes, much worse than either the fresh saliva or the fresh aqueous humour of the animal experimented on. By sticking to the glass slide a ring of thin paper, and mounting the object in the centre of this, the cover-glass can rest all round on the paper, and hurtful pressure on the tissue be avoided. If the specimens so obtained preserve their normal appearance for a time sufficiently long for observation, the changes in the minute structure of the gland-cells can obviously be followed by taking pieces from glands in various stages of activity. Although it is unlikely that no change should take place in the cells thus treated, the normal appearance is, I think, almost exactly preserved, for the following reason. In the rabbit the parotid gland is divided into three main portions 1, the tonnecting part between the upper and lower divisions has many lobules thin enough to be seen through. Either portion, after the vessels running to it have been tied and cut, can be pinned out on a piece of gutta-percha and the connecting part drawn away from the body. The thinner lobules of the connecting portion can then be viewed under the microscope with the blood freely circulating'. It is better to pin back the lower, rather than the upper division. The gland-cells can thus be watched in the living condition for many hours. I have. tried the method, used by Kuhne and Lea' for the pancreas, of running continually sodium chloride solution at 380 C. over the tissue, but as yet with no very satisfactory results; the connective tissue between the lobules has a great tendency to swell up into a jelly, and so hinder a defined view of the gland-cells. This is, bowever, probably due to insufficient care for the proper preservation of the correct temperature. That the gland-cells in the pinned-out gland are practically un- injured results from.the facts, that the blood continues to flow actively around them, and that injection of pilocarpin or stimulation of the sympathetic nerve in the neck causes a flow of saliva and an alteration 1 Cp. Krause, Die Anat. des Kaninchens, s. 151. 2 I may mention for the sake of those working on vaso-motor nerves in muscle that the blood circulation in the thin muscular layer of the platysma in the neck can be seen in a similar manner without difficulty. This and probably other thin muscles of the rabbit or rat would afford peculiar advantages for watching the vaso-dilator or vaso-con- strictor effects of nerves distributed to muscle. 3 Op. cit. CHANGES IN SEROUS GLANDS DURING SECRETION. 263 in the appearance of the glands. The effect of stimulating the sympa- thetic nerve on the circulation is most striking, the arteries contract and the blood-flow in the capillaries all but stops. The gland-cells viewed in this way shew all the characters in rest and activity which they shew in freshly-made mounted specimens in corresponding states. Mounted specimens then from the fresh parotid gland do give unaltered the living gland appearances 1. There is, I think, no reason to believe that the sub-maxillary, infra-orbital, or lachrymal glands behave differently. The Parotid Gland of the Rabbit. The alveoli of the parotid of a huingry rabbit taken fresh from the animal and at once examined, are granular throughout (P1. VII. Fig. 1); there is no division into an outer clear and an inner granular zone; the cells of the alveoli can be made out with more or less distinctness as clear lines running between the granules. These clear spaces are less distinct in the gland with circu- lation than in the mounted specimen; the outlines never appear as dark lines as they dQ in hardened glands. The granular state of the fresh gland has been noticed by Pfltlger2 and other observers. But if the gland be thrown for some time into a state of activity either by stimulating the sympathetic in the neck, or by injecting pilocarpin, or by feeding, the alveoli alter their appearance, and instead of being granular throughout become clear at their outer portion near the basement mem- brane, and thus shew an inner granular and an outer clear, non-granular, zone. That is, during secretion the granules normally contained by the cells, are in some way or other used up, probably to form part of the saliva secreted. The relative effects of stimulating the cerebral and sympathetic nerves I have not yet satisfactorily made out, though it has seemed to me that the sympathetic has the more rapid influence. The longer the gland is stimulated the more obvious the outer clear zone becomes, so that at length some alveoli may shew scarcely any 1 The chief results of this paper were obtained in April of this year from mounted specimens of fresh tissues. I delayed the publication however, because of some doubt as to the amount of change from the normal state caused by the method. 2 Stricker's Histology. Translated by Dr Power. Vol. x. p. 425. 264 J. N. LANGLEY. granules. (Fig. 4.) At this stage the secretion offered by the gland is very scanty. During the secretion the outlines of the cells become more evident, especially towards the lumen; the outlines then more- over being usually marked by lines of granules; the lumina become obvious and stretch out a short distance between the cells: the cells are thus slightly separated at their inner borders. As the granules disappear from a cell the rest of the granules do not form a small collection at the part bordering the lumen, but form rather lines at the margin and sides near the lumen (cp. Figs. 2, 3 and 4). The cells too, as has been pointed out by Heidenhain 1, become smaller. The changes in the gland in an adult rabbit can be readily seen during digestion; they are perceptible an hour or two after feeding, and persist for some time; indeed it is probable that an adult rabbit, kept supplied with ample food, always shews a beginning clear zone; so that the throughout-granular condition belongs only to the fasting animal. Apparently after one to two days' hunger, the granular substance, which has been stored in the alveolar-cells, begins to be used up, so that, from that time on, the gland presents as regards granules more and more of a digesting appearance. Specimens mounted in an indifferent fluid rapidly lose their normal appearance; water is imbibed, the background of the cells becomes brighter, and many granules somewhat larger and more distinct; in addition to this, some granules appear to be dissolved and fresh ones to be formed. About ten to twenty minutes after mounting in any fluid the resting and active gland become much more alike; in the former the outer border becomes clearer, in the latter it becomes more granular; if mounted without addition of fluid, the differences in the gland in its two states are preserved for a considerable time. I have attempted to reproduce the appearance offered by the gland as the cells become acted on by the fluid. Fig. 5 (P1. VII.) is from a resting gland ten minutes after being mounted in saliva. Fig. 6 from a resting gland twenty minutes after being mounted in saliva. The clear border appearing at a certain stage of the action of the fluid on the alveoli is totally different in appear- ance from the "non-granular" zone appearing in the alveoli on stimu- lation.