CONSTEUCTION OF SECEETING GLANDS. 237 



form of loops ; in the kidney, little round tufts of fine blood-vessels 

 project into terminal or lateral dilatations of the ducts, but without 

 0})ening into them. 



The human liver does not precisely agree in structure with either of 

 the above classes of compound glands. Its ducts, which are neither 

 coiled nor sacculated, would seem to begin within its lobules, in form 

 of a network of excessively fine channels which run between the sides 

 of contiguous polyhedral cells, and these occupy the interstices of the 

 reticular capillary blood-vessels, which also are peculiar, inasmuch as 

 they receive and transmit venous blood. 



Besides blood-vessels, the glands are furnished with lym])hatics, which in 

 some compound glands proceed from interstitial lymphatic spaces within, 

 as already stated (p. 1S5). Branches of nerves have also been followed, 

 for some way, into these organs, and the well-known fact, that the flow 

 of 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 that an increased 

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

 Moreover, fine non-medullated nervous fibres have in several instances 

 been described as forming a network between the alveolar cells ; and in 

 the salivary glands, Pfliiger has affirmed a direct passage of nerve-fibres, 

 both medullated and non-medullated, into the secreting cells : his ob- 

 servations, however, have not been corroborated by other inquirers. 



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

 a gland consists of the ducts, blood-vessels, lymph-vessels and lacuna;, 

 and a few nerves, in some cases connected by an intervening 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 tcazed out ; but then it is sufficiently protected and 

 supported by a fibrous capsule on the outside, and 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 ramifica- 

 tions. The substance of the kidney contains scarcely any well-cha- 

 racterised fibrous connective tissue, except bundles which here and 

 there accompany the larger branches of vessels, but there is an abun- 

 dant, though very delicate, network of retiform tissue in a soft amor- 

 phous 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 some- 

 times 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 connec- 

 tive 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 

 membrane, or upon the surface of the skin. They are sometimes 

 provided with a reservoir, in which the secretion is collected, to be 



