GLAND. 



489 



Miiller expressly says, that in no organ are the 

 J'ree extremities of the bloodvessels seen, but 

 that the arteries always j)ass by u reticulate 

 anastomosis into the veins; that the blood cir- 

 culates between the secreting canals of the 

 liver, and at length on their surface, so as, as it 

 were, to soak their coats with blood, but it does 

 not pass into the canals themselves; or, in 

 other words, that the sanguiferous vessels are 

 not continuous with the biliary tubes.* 



The important investigations of Kiernan 

 respecting the minute anatomy of the liver, 

 have shewn that the vena portae having divided 

 so as to constitute an intricate plexus in each 

 lobule of the organ, and having ramified on 

 the secreting canals, terminates in the hepatic 

 vein.f In the section on the development 

 further evidence is furnished in corroboration 

 of these observations. 



In all the^e instances, then, it is proved that 

 there is no continuity between the arteries and 

 the secreting tubes; and as the smallest secreting 

 canals are always considerably larger than the 

 smallest bloodvessels, the proportion varying 

 in different glands, it may be assumed that in 

 the whole glandular system, the arteries, having 

 divided to a great degree of minuteness, and 

 having ramified freely on the surface of the 

 secreting canals, terminate directly in the re- 

 turning veins. 



Although in former times such a disposition 

 of the bloodvessels as that now described 

 would have been regarded as incompatible 

 with the process of secretion, yet since the 

 interesting researches of Dutrochet on Endos- 

 mose and Exosmose,^ there is no difficulty in 

 understanding that fluids may readily pass 

 from the interior of the arteries into the se- 

 creting canals without there being any direct 

 communication between these two orders of 

 tubes. Not only may this passage take place, 

 but even it is rendered probable by the experi- 

 ments of Magendie that the bibulous matter 

 constituting the glandular texture, and present- 

 ing, as we have found, so many varieties in its 

 physical characters, may separate fluids, varying, 

 according to the gland employed, from the 

 diversified substances mechanically mixed toge- 

 ther and suspended in the blood. 



Lymphatic vessels. Notwithstanding these 

 are readily traced in the larger glands, their 

 disposition, and especially their origin, are not 

 known ; a connexion, however, has been rather 

 generally admitted in certain glands between 



De Gland. Struct., p. 74, 12. Phys. des 

 Menschen, 1 Band, p. 441. 



t Phil. Tran. 1833, p. 745. Mr. Kiernan infers 

 that the hepatic artery terminates, not as is usually 

 supposed in the vena hepatica, but in the vena 

 portae. Miiller, however, thinks it is not probable 

 that this is the true disposition, because the prepa- 

 rations of Leiberkuhn show that the capillary 

 branches of the venae hepaticae can be as readily 

 injected from the hepatic artery as from the hepatic 

 vein. Notwithstanding these objections, analogy 

 would induce us to suppose that Mr. Kiernan is 

 correct in his supposition. 



J Nouv. Keener, sur 1'Endos. et 1'Exosmose, 

 1828. 



$ Lect. on the Physical Conditions of the Tissues, 

 Lancet, 1834-35. ' 



their ducts and the lymphatics. In one instance 

 Cruikshank tilled the absorbents of the mamma 

 from the lactiferous ducts ; and both Walter 

 and Kiernan contend that the absorbents of the 

 liver may be injected from the biliary ducts. 

 Miiller, on the contrary, denies this commu- 

 nication, and states that the lymphatics are 

 much larger than the smallest secreting canals. 

 He also contends as to the results of injections, 

 that the arguments drawn from them have no 

 greater weight than all others derived from the 

 fortuitous passage by rupture of fluids from 

 one into a different order of vessels. 



Nerves. In proportion to their size the 

 glands, like the other organs of the vegetative 

 functions, receive very small nerves, which are, 

 with some few exceptions, derived from the 

 system of the great sympathetic. The nervous 

 fibrils surround and accompany the branches 

 of the arteries, till, in the interior of the gland, 

 they become so minute that it appears impossi- 

 ble to detect their exact termination. Miiller 

 states that they never separate from the blood- 

 vessels, and, consequently, that they do not 

 supply the proper glandular substance. But in 

 such a case as this the evidence afforded by 

 microscopical inspection alone should be re- 

 ceived with great reserve, especially when it is 

 recollected that in opposition to the doubtful 

 information thus acquired must be placed the 

 unquestioned fact that the mind is capable of 

 influencing the contraction of the secreting and 

 excreting tubes, as is instanced in the flow of 

 the saliva, of the tears, and of the semen under 

 certain mental impulses. But perhaps a still 

 more striking illustration of the control of the 

 nervous system is afforded by the discharge of 

 several glandular fluids resulting from impres- 

 sions acting on comparatively remote but 

 associated surfaces the pouring forth of the 

 saliva for example, in consequence of the con- 

 tact of various substances with the tongue ; of 

 the bile and pancreatic juice from the applica- 

 tion of food to the surface of the duodenum ; 

 of the semen from the stimulation of the glans 

 penis. In all these and similar instances it 

 must be presumed from analogy that the effect 

 of the physical impression is conveyed through 

 the only known media of conduction, the 

 nerves.* The iacts here adduced respecting 

 the influence of the nerves merely relate to the 

 contraction of the secreting and excreting 

 canals ; how far the nervous energy is essential 

 to the process of glandular secretion itself be- 

 longs to another division of the subject. (See 

 SECRETION.) 



Interstitial cellular tissue. A considerable 

 portion of every gland is made up of the con- 

 necting cellular membrane, which, as in all other 

 organs, enters the interior, where it fills up all 

 the minute fissures and angles that intervene 

 between the tubes and lobules, and at length, 

 penetrating between the most minute of the 

 secreting canals, it constitutes a nidus for the 

 lodgement of the constituent parts. 



The investing membrane is in many instances 



* I have in another place entered more fully 

 upon this question : Obs. on the Struct, and Funct. 

 of the Spinal Cord, p. 136, et seq. 



