102 LECTURE IV. 



enabled by the contraction of these fibres to grow narrower 

 or shorter. This narrowing of their channel may have 

 the effect of impeding transudation of fluids, whilst, on 

 the contrary, in the case of the relaxation or paralysis of 

 the muscular fibres, the widening of the vessel may 

 favour such transudation. Let us admit this for the pre- 

 sent, but allow me, before proceeding farther, to enter 

 somewhat into the analysis of the mass of tissue which 

 lies around the vessels, and is generally conceived to be 

 of a very simple and uncomplicated nature. 



If we select parts where the vessels lie very closely 

 packed, and there is perhaps nearly as much vessel as 

 tissue, as, for example, the liver, in which this condition 

 really does occur (for a liver, when its vessels are full, 

 contains nearly as large a volume of vessels as it does of 

 proper hepatic substance), we see that the interstices 

 which are left between the vessels are filled with quite a 

 small number of cells. 



If we examine a single acinus of the liver by itself, 

 we find, when a very lucky transverse section has been 

 obtained, in its centre the FlG< 28 



vena centralis or intralobula- 

 ris, which runs into the hepa- 

 tic vein, at the periphery 

 branches of the portal vein, 

 which send capillary twigs in- 

 to the interior. These at 

 once form a network, which 

 at first has long, but after- 

 wards more regularly shaped, meshes, and extends in 

 the direction of the central (or hepatic) vein, and at last 

 terminates in it. The blood, therefore, after it has en- 



Fig. 28. Section from the periphery of the liver of a rabbit ; the vessels com- 

 pletely injected. 11 diameters. 



