328 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



the character of the blood, (i) We have said that that 

 which is taken up by the capillaries passes into the vena 

 porta. Now this is a quite unique and exceptional vein. 

 All other veins ramify at one end only ; this at both 

 ends. All other veins, after receiving their supply by 

 the capillaries from the tissues, empty by an open mouth 

 into the general circulation. This one receives its sup- 

 ply from the capillaries of the intestines, the stomach, 

 and the spleen, and then, instead of emptying into the 

 vena cava, close at hand, goes to the liver, to be again 

 distributed by inverse capillary ramification through that 

 organ, and gathered a second time by the capillaries of 

 the hepatic vein, and so delivered to the general circu- 

 lation. Thus there is a mesenteric artery, but no corre- 

 sponding mesenteric vein. There is a splenic artery, but 

 no splenic vein. The vena porta takes the blood of both 

 these, and carries it to the liver, to be again distributed 

 there. This is shown in the diagram (Fig. 210). Now, 

 during the passage of the digested food through the 

 liver it undergoes an important change, preparing it for 

 immediate use in the generation of force and heat. In 

 other words, it is sanguined- — i. e., made into material 

 suitable for circulation in the blood. The nature of this 

 important change we will explain more fully when we 

 come to speak of the functions of the liver (page 446). 



That part of the dissolved food which is taken up by 

 the lacteals, as we have seen, is carried through the mes- 

 enteric glands before reaching the thoracic duct. In 

 these glands an important change takes place. After 

 passing through these it is no longer mere dissolved 

 food — i. e., peptones and fats — but apparently a living 

 fluid like the blood, although not yet red. Before pass- 

 ing through the glands it is noncoagulable ; after pass- 

 ing it is coagulable, like the blood. Before passing it 

 contains no globules except fat globules. After passing 



