II 



EXTERNAL DIGESTIVE SECRETIONS 



131 



woman), with an average volume of 1720 c.c. (Vierordt). This 

 gigantic development, and the intimate relations by means of the 

 portal system with the gastro-intestinal system, point to the true 

 physiological function of the liver as a laboratory for complex and 

 mysterious chemical operations, in which the preparation of the 

 bile that is formed and poured out into the gall - bladder and 

 duodenum is probably only a secondary process. The amount of 

 bile secreted daily by man rarely, in fact, exceeds 800 grins., while 

 the little parotid gland (which only weighs 24-30 grms.) daily 

 discharges as much as 1000 grms. of secretion. In this chapter, 

 however, we shall only consider the liver as the organ of Hie 



Fio. 40. Diagram of fragment of liver from a six -months' foetus. Silver chromate method. 

 (G. Retzius.) The bile canaliculi are stained black. They have not yet anastomosed, and 

 give off minute twigs between the hepatic cells, with a terminal dilatation. 



secretion. Its complex metabolism and internal secretions will be 

 discussed elsewhere. 



Morphologists regard the liver as a tubular retiform gland, 

 consisting of cells arranged round glandular spaces which form a 

 very fine capillary network, the bile canaliculi. These appear to 

 have no membrane propria, and to be merely grooved out between 

 adjacent liver-cells, running on into the bile ducts, which have 

 walls and unite in larger and larger branches, till they converge 

 into the excretory, hepatic duct. 



In the lower vertebrates, and the embryos of birds and 

 mammals, the liver is a tubular gland. The tubules do not 

 anastomose to form a network, but end in small branches, the ends 

 of which are often enlarged and penetrate into the hepatic cells 

 (Fig. 46). In adult vertebrates, on the contrary, the ramifications 

 of the canaliculi do anastomose to form an intercellular network, 

 which communicates with special vacuoles in the cell protoplasm 



