CHAP, in.] METABOLIC PROCESSES OF THE BODY. 743 



cuticle. Where the surface of a cell abuts on a blood vessel the 

 substance of the cell is generally separated from the wall of the 

 vessel by a lymph-space, which is connected with the hepatic 

 lymphatic vessels. 



The cell-substance itself, as might be expected from what has 

 been already urged concerning the metabolism going on in the 

 liver, presents appearances which differ very widely according to 

 circumstances. Sometimes the cell-substance appears dense, com- 

 pact and of fairly uniform texture, though more or less granular ; 

 the whole cell is then of relatively small bulk. Sometimes the 

 cell-substance appears large and bulky, owing to its being largely 

 loaded with a substance staining red-brown with iodine, which we 

 shall study in detail presently, called glycogen. When such a 

 cell is hardened and the glycogen dissolved out, the cell-substance 

 appears to be so completely riddled with vacuoles, as to be reduced 

 to a mere shell surrounding a loose irregular network except im- 

 mediately round the nucleus, where it is more solid. But it will 

 be best to reserve the discussion of these changes in the cells until 

 we have studied to some extent the metabolic changes which take 

 place in the liver. We may add however that very frequently, 

 especially in certain animals, the hepatic cell is crowded with oil 

 globules of various sizes ; these are at times so numerous as com- 

 pletely to hide the nucleus, which cannot be seen until the fat has 

 been removed. 



450. Where the sides of two hepatic cells are in contact, 

 careful examination with high powers of the microscope will often 

 reveal, at about the middle of the line of junction of the two sides, 

 a minute hole, a tenth or less of the diameter of the cell, which 

 according to some observers is lined with a delicate cuticular 

 lining. This hole is the section of a minute canal passing between 

 the two cells in the middle line of their apposed surfaces. A model 

 of it might be made on two small blocks of chalk by cutting a 

 narrow semicircular groove down the middle of one side of each 

 block, and then bringing these two sides into accurate contact. 



We have already said ( 416) that the blue colouring matter, 

 sodium sulphindigotate, when injected into the veins is excreted 

 by the liver as well as by the kidney. If the animal be killed at 

 an appropriate time after the injection and the liver hardened 

 and prepared, sections of the liver will, in successful specimens, 

 reveal a close set network of blue thin lines traversing the whole 

 of each of the lobules. The meshes of the network are of about 

 the width of a hepatic cell ; and upon examination it will be found 

 that the empty minute holes, just spoken of as seen in the sections 

 of a liver prepared in the ordinary way, are now filled with the 

 blue pigment; the minute canal of which each hole is a section 

 is a part of a network of minute canals, passing between the cells 

 in various directions all over the lobule. They may be traced to 

 the edge of the lobule, and at various points of the margin the 



