244 AN AMERICAN TEXT-ROOK OF PHYSIOLOGY. 



bringing the ends to the abdominal wall to form fistulous openings. The 

 secretion thus obtained contains diastatie and also inverting ferments, the action 

 of which is described on p. 308. Histologically, the cells in the bottom of 

 the crypts do not possess the general characteristics of secreting cells. 



D. Liver ; Kidney. 



The liver is a gland belonging to the compound tubular type. The 

 hepatic cells represent the secretory cells and the bile-ducts carry off the 

 external secretion, which is designated as bile. In addition it is known that 

 the liver-cells occasion important changes in the material brought to them 

 in the blood, and that two important compounds, namely, glycogen and urea, 

 are formed under the influence of these cells and afterward are given off to 

 the blood-stream. The liver, then, furnishes a conspicuous example of a 

 gland that forms simultaneously an external and an internal secretion. In 

 this section we have to consider only certain facts in relation to the external 

 secretion, the bile. 



Histological Structure. — The general histological relations of the hepatic 

 lobules need not be repeated in detail. It will be remembered that in each 

 lobule the hepatic cells arc arranged in columns radiating from the central 

 vein, and that the intralobular capillaries are so arranged with reference to 

 these columns that each cell is practically brought into contact with a mixed 

 blood derived in part from the portal vein and in part from the hepatic 

 artery. 



As a gland making an external secretion, the relations of the liver-cells to 

 the ducts and to the nervous system are important points to be determined. 

 The bile-ducts can be traced without difficulty to the fine interlobular branches 

 running round the periphery of the lobules, but the finer branches or bile- 

 capillaries springing from the interlobular ducts and penetrating into the in- 

 terior of the lobules have been difficult to follow with exactness, especially as to 

 their connection with the interlobular ducts on the one hand, aud with the 

 liver-cells on the other. The bile-capillaries have long been known to pene- 

 trate the columns of cells in the lobule in such a way that each cell is in con- 

 tacl with a bile-capillary at one pointofits periphery, and with a blood-capil- 

 lary at another, the bile- and blood-capillaries being separated from each other 

 by a portion of the cell-snbstance. But whether or not intracellular blanches 

 from these capillaries actually penetrate into the substance of the liver-cells 

 ha- been a matter in dispute. Knppfer contended that delicate ducts arising 

 from the capillaries enter into the cells and end in a small intracellular vesicle. 

 As this appearance was obtained by forcible injections through the bile-duets, 

 it was thought by many to be an artificial product; but recent observations 

 with staining reagents tend to substantiate the accuracy of Kuppfer's # obser- 

 vations and confirm the belief that normally the system of bile-duct- begins 

 within the liver-oil- in minute channels that connect directly with the bile- 

 capillaries. 



Two questions with reference to the bile-ducts have given rise to considerable 



