210 THE MUCOUS MEMBRANES 



of small solid bodies, often of a flattened lenticular form, bnt varyinj]^ 

 nmch both in shape and size, and i)laced at different depths below the 

 mucous membrane on which their ducts open. The glands of Brunner, 

 which form a dense layer in the commencing part of the duodenum, are 

 of this kind. 



3. SoJitnrji and agminafed glanrh, conrihhaic glands (\ler\le), follkidar 

 glands (Kiilliker), IgmpJiofd glands. — Found in various jjarts of the 

 alimentary mucous membrane. They may be single (soJifarg 

 glands), or in patches {agminated glands), and commonly extend 

 down into the submucous tissue. They are small rounded bodies con- 

 sisting of fine retiform tissue, supporting radiating blood-capillaries, 

 with lymph-corpuscles in the meshes, and communicating with similar 

 tissue (lymphoid tissue) diffused in the adjacent part of the membrane. 

 Several of these follicles are sometimes ])laced round a recess of the 

 mucous membrane which opens on the surface, and which may be 

 simple, as in certain glands at the root of the tongue and in the pharynx, 

 or complex and multilocular, as in the tonsils. 



These lymphoid follicles, although designated as glands, pour out no secretion 

 on a surface. They are to be regarded as dependencies of the lymphatic system, 

 and as probably concerned in the production of IjTnph corpuscles. At all events, 

 the Ipnphatics are extremely abundant in their immediate neighbourhood, and in 

 some places form a kind of sinus closely surrounding the follicle. 



The mucous membranes are supplied with nerves, and endowed 

 with sensibility ; but the proportion of nerves which they receive, 

 as well as the degree of sensibility which they possess, differs very 

 greatly in different parts. The mode of distribution and termination 

 of these nerves will be dealt with in describing the special anatomy of 

 the parts where they occur. 



Secretion. — Mucus is a more or less viscid, transparent, or slightly turbid fluid, 

 of variable consistency. It is somewhat heavier than water, though expectorated 

 mucus is generally prevented from sinking in that liquid by entangled air- 

 bubbles. Examined with the microscope, it is found to consist of a fluid, con- 

 taining solid particles of various kinds, viz., 1. Epithelium particles detached by 

 desquamation ; 2. Corpuscles resembling the pale corimscles of the blood ; o. 



Granules and molecules occasionally. The visci- 

 Fig. 139*. dity of mucus depends on the liquid part, which 



contains a peculiar substance, named by the 

 chemists mxei/i. This ingredient is precipitated 

 and the mucus rendered turbid by the addition of 

 water or a weak acid, but it may be partly redis- 

 solved in an excess of water, and completely so in 

 a strong acid. This mucin is solulile in alkalies, 

 and its acid solutions are not precipitated by 

 ferrocyanide of potassium. Little can, of coui'se, 

 be expected from a chemical analysis of a hetero- 

 geneous and inseparaljle mixture of solid particles 

 with a liquid solution, such as we find in mucus. 

 Pig. 139*. — Goblet-Cells FROM which is, moreover, subject to differences of 

 Trachea of Rabbit. Highly quality according to the part of the mucous 

 Magnified (Klein). membrane whence it is derived. Examined thus, 



however, nasal mucus has been found to yield, 

 besides water and mucin, alcohol-extract with alkaline lactates, water-extract 

 with traces of albumin and a phosphate, chlorides of sodium and potassium, 



