SECRETING GLANDS. ccxxv 



secretion in several glands is affected by mental emotions, shows that an 

 influence is exerted on secreting organs through the medium of the nervous 

 system ; and this is further shown by the fact, now ascertained, that an in- 

 creased flow may be brought on by direct or reflex stimulation of their 

 nerves. The distribution of these nerves in the salivary glands has been 

 recently traced by Pfliiger. He finds that dark-bordered nerve-fibres pro- 

 ceed to the csscal glandular saccules ; that the membranous tube of the 

 nerve-fibre becomes continuous with the membrana propria of the saccule, 

 whilst the fibre, retaining its dark borders, passes into the saccule and divides 

 into fine branches, which run between the nucleated gland-cells lining it, 

 and finally penetrate the walls of these cells and become connected with 

 their nuclei. Other nerve-fibres proceeding to the saccules come from 

 ganglionic or nerve-cells ; these fibres are chiefly pale or non-medullated, 

 though not without admixture of the dark bordered kind, and are sup- 

 posed to belong to the sympathetic system. These ganglionic fibres have 

 also been traced to the gland-cells. 



From what has been stated, it will be apparent that the substance of a 

 gland consists of the ducts, blood-vessels, lymph-lacunse, and a few nerves, 

 in some cases connected by an interveniug tissue. In the testicle there is a 

 very small amount of intermediate connective tissue, which, with the aid of 

 the blood-vessels, holds the tubules but feebly together, so that the structure 

 is comparatively loose, and readily admits of being teazed out ; but then it 

 is sufficiently protected and supported by a fibrous capsule on the outside, 

 atid fibrous septa within the gland. In the racemose glands there is a good 

 deal of uniting connective tissue, which surrounds collectively each group of 

 saccules, binds together the lobules, and supports the vessels in their ramifi- 

 cations. The substance of the kidney contains scarcely any well characterised 

 fibrous connective tissue, except bundles which here and there accompany 

 the larger branches of vessels, but there is an abundant, though very deli- 

 cate, network of retiform tissue in a soft, amorphous matter between the 

 tubules and blood-vessels, which binds them together. 



Parenchyma is a term sometimes employed in describing glandular organs, 

 though it is less in use now than formerly. It is used sometimes to denote 

 the solid part of a gland composed of the various tissues already mentioned ; 

 at other times to signify any substance, of whatever nature, lying between 

 the ducts, vessels, and nerves. In this last sense, the parenchyma is in 

 certain glands represented by connective tissue, in others by corpuscles and 

 amorphous matter, whilst in some it can scarcely be said to exist. 



Some glands have a special envelope, as in the case of the kidney and 

 testicle ; others, as the pancreas, have none. 



The ducts of glands ultimately open into cavities lined by mucous mem- 

 brane, or upon the surface of the skin. They are sometimes provided with 

 a reservoir, in which the secretion is collected, to be discharged when the 

 purposes of the economy so demand. The reservoir of the urine receives 

 the whole of the secreted fluid ; in the gall-bladder, on the other hand, only 

 a part of the bile is collected. The vesiculse seminales afford another 

 example of these laterally appended reservoirs. The ducts are constructed 

 of a basement-membrane and lining of epithelium, and in their smaller 

 divisions there is nothing more ; but in the larger branches and trunks a 

 fibro- vascular layer is added, as in the ordinary mucous membrane, with 

 which many of them are continuous, and with which they all agree in 

 nature. A more or less firm outer coat, composed of connective tissue, 

 comes, in many cases, to surround the mucous lining, and between the two, 



