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



those of blood-serum on the other. But perhaps the most striking 

 feature of the spleen-pulp is its richness in the so-called ex- 

 tractives. Of these the most common and plentiful are succinic, 

 formic, acetic, butyric and lactic acids, inosit, leucin, xanthin, 

 hypoxanthin and uric acid. Tyrosin apparently is not present in 

 the perfectly fresh spleen, though leucin is : both are found when 

 decomposition has set in. The constant presence of uric acid is 

 remarkable, especially since it has been found even in the spleen 

 of animals, such as the herbivora, whose urine contains none. 



The richness of the spleen in these extractives is an indication 

 of the importance of the metabolic events with which the organ 

 has to do ; but it will be more profitable to discuss what goes on 

 in the spleen in connection with the metabolic changes in other 

 parts of the body, in the liver for instance, than to attempt to lay 

 down any so-called 'functions' of the spleen. When we confine 

 our attention to the spleen itself we learn very little ; thus the 

 whole organ may be successfully removed without any very obvious 

 changes in the economy resulting. We may return therefore to 

 the discussion of the formation of the bilirubin of bile, and of the 

 changes undergone by haemoglobin, with which as we shall see the 

 spleen is connected, and which moreover has to do with the 

 formation of other pigments. 



