22 THE SPLEEN. 



Arterial blood becomes venous by contact with living 

 protoplasm. Venous blood is distinguished from arterial 

 by its crimson colour, its slight dichroistn, the less propor- 

 tion of oxygen which is associated with its haemoglobin, its 

 large proportion of combined CO 2 , its less proneness to 

 coagulation, and by containing fewer blood-corpuscles. 

 Venous blood differs somewhat in composition according to 

 its source. As compared with ordinary venous blood, that 

 of the hepatic vein contains less albumin and more ex- 

 tractives (e.g., urea and grape-sugar). In that of the splenic 

 vein, also, differences exist, which indicate that in this 

 organ the coloured blood-corpuscles are disintegrated, and 

 colourless corpuscles formed. 



The Spleen. 



The following are the facts best ascertained as to the 

 spleen-pulp, and the blood which flows from it : 



The spleen-pulp contains much haemoglobin, to which 

 the richness of its ash in iron is due (Malassez). The 

 aqueous extract of spleen-pulp contains uric acid, and the 

 allied body hypoxanthin, in quantities which, although 

 very small, are larger than those met with in any other 

 tissue (Strecker). The splenic blood contains fewer blood- 

 disks and more colourless corpuscles than the blood of any 

 other organ. There exist in the spleen structures which 

 are destined to become colourless corpuscles. It also con- 

 tains structures which are concerned in the breaking up of 

 blood-disks, and are the sources of the pigment with which 

 the pulp is provided. The enlargement of the spleen 

 which takes place a few hours after every considerable 

 meal, is chiefly if not entirely due to vascular dilatation 

 (Hosier). 



