SECRETION. 185 



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

 The bile-ducts can be traced without difficulty to the fine iuterlobular 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, auofwith 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- 

 tact with a bile-capillary at one point of its 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-substance. But whether or not intracellular branches 

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

 has been a matter in dispute. Kuppfer 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-ducts, 

 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-ducts begins 

 within the liver-cells in minute channels which connect directly with the 

 bile-capillaries. 



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

 discussion and investigation : first, the relationship existing between the liver- 

 cells and the lining epithelium of the bile-ducts ; second, the presence or ab- 

 sence of a distinct membranous wall for the bile-capillaries. Different opin- 

 ions are still held upon these points, but the balance of evidence seems to show 

 that the bile-capillaries have no proper wall. They are simply minute tubular 

 spaces penetrating between the liver-cells and corresponding to the alveolar lu- 

 men in other glands. Where the capillaries join the interlobular ducts the liver- 

 cells pass gradually or abruptly, according to the class of vertebrates examined, 

 into the lining epithelium of the ducts. From this standpoint, then, the liver- 

 cells are homologous to the secreting cells of other glands in their relations to 

 the general lining epithelium. Several observers (MaCallum, 1 Berkeley, 2 and 

 Korolkow 3 ) have claimed that they are able to trace nerve-fibres to the 

 liver-cells, thus furnishing histological evidence that the complex processes oc- 

 curring in these cells are under the regulating control of the central nervous 

 system. According to the latest observers (Berkeley, Korolkow) the terminal 

 nerve-fibrils end between the liver-cells, but do not actually penetrate the sub- 

 stance of the cells, as was described in some earlier papers. If these observa- 

 tions prove to be entirely correct they would demonstrate the direct effect of 

 the nervous system on some at least of the manifold activities of the liver- 

 cells. So far as the formation of the bile is concerned we have no satisfactory 

 physiological evidence that it is under the control of the nervous system. 



Composition of the Secretion. The bile is a colored secretion. In 



1 MaCalluro : Quarterly Journal of the Microscopical Sciences, 1887, vol. xxvii. p. 439. 



2 Berkeley : Anatomvscher Anzeiger, 1893, Bd. viii. S. 769. 3 Korolkow: Ibid., S. 750. 



