3i3 A MANUAL OF PHYSIOLOGY 



the liver, and a tide of blood like that which passes through 

 the portal vein. And, as we shall see, the liver has other 

 functions, some of them certainly of at least equal im- 

 portance with the secretion of bile, and one of them 

 evidently requiring from its very nature a bulky organ. 

 Accordingly, both the richness of the blood-supply and the 

 size of the secreting cells are out of proportion to the calibre 

 of the ultimate channels that carry the secretion away. 

 The so-called bile-capillaries, which represent the lumen of 

 the secreting tubules, are mere grooves in the surface of 

 adjoining cells ; and the architectural lines on which the 

 liver lobule is built are : (i) the interlobular veins which carry 

 blood to it ; (2) the rich capillary network which separates 

 its cells and feeds them ; (3) the central intra-lobular vein 

 which drains it. Thus a network of cells lying in the meshes 

 of a network of blood-capillaries takes the place of a regular 

 dendritic arrangement of ducts and tubules ; and in accord- 

 ance with this the bile - capillaries, instead of opening 

 separately into the ducts, form a plexus with each other 

 within the hepatic lobule. 



The ducts and secreting tubules of all glands are lined by 

 cells of columnar epithelial type, but the type is most closely 

 preserved in the ducts. In none of the digestive glands is 

 there more than a single complete layer of secreting cells. 

 But the alveoli of the mucous salivary glands show here and 

 there a crescent-shaped group of small deeply-staining cells 

 (crescents of Gianuzzi) outside the columnar layer (Plate II., 

 i, 3), and between it and the basement membrane, while 

 the gland-tubes of the cardiac end of the stomach have in 

 the same situation a discontinuous layer of large ovoid cells, 

 termed parietal from their position, oxyntic (or acid-secreting) 

 from their supposed function (Fig. 104). The serous salivary 

 glands, the pancreas, the pyloric glands of the stomach, the 

 Lieberklihn's crypts, have but a single layer of epithelium ; 

 and since there is no hepatic cell which is not in contact 

 with at least one bile-capillary, the liver may be regarded as 

 having no more. Remarkable histological changes, evidently 

 connected with changes in functional activity, have been 

 noticed in most of the digestive glands. In discussing these, 



