62 



ZOOLOGY. 



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Fig. 23. DIAGRAM OF STRUCTURE OF 

 LIVER. 



(After Huxley.) 



that has been suitably stained, under the microscope, we 

 shall see that each lobule appears at first sight to be made 

 up of a mass of nucleated cells, the liver-cells, without any 



large intercellular spaces. 

 More careful examination 

 shows that very small spaces 

 occur between some of the 

 cells spaces much smaller 

 than the cells themselves. 

 It is possible to prove that 

 these are really the ultimate 

 branches of the bile-ducts. 

 This is done by the method 

 of injection : some coloured 

 liquid is forced by a pump 

 into the bile-duct of a fresh liver, and on cutting thin 

 sections the colour is found to fill these tiny spaces 

 between the cells. In reality then the liver- cells are the 

 epithelial cells of these narrow tubes, and we have here a 

 remarkable case in which the epithelial cells are larger 

 than the cavity they enclose. The change from ordinary 

 epithelial cells in one of the bile-ducts to liver-cells is 

 shown in fig. 23. These minute ultimate branches of the 

 bile-ducts are called the bile-capillaries a rather dangerous 

 term, as they have nothing to do 

 with blood- capillaries. 



The method of injection may 

 also be applied to trace the 

 blood-vessels in the liver. The 

 branches of the hepatic artery 

 and portal vein end in small 

 vessels which lie in the connective 

 tissue that surrounds each lobule 

 and separates one lobule from 

 another : they are therefore called 

 inter -lobular vessels. The ultimate 



factors of the hepatic vein, on the other hand, penetrate 

 into the centre of every lobule : they are intra-lobular. 

 Between the liver-cells is a network of blood-capillaries, 

 which at the margin of the lobule are connected with the 



Fig. 24. DIAGRAM OF TUB 



BLOOD-VESSELS OF A LOBULE OF 



THE LIVER. 



