334 THE ADRENAL, GENERAL MOTOR, AND VAGAL SYSTEMS. 



four in the subhepatic vein is to one in the portal vein, after 

 the blood has been submitted to the effects of hepatic func- 

 tions. It seems clear, therefore, that red corpuscles are de- 

 stroyed both in the spleen and in the liver, and that, since 

 the spleen is possessed of no external duct, it is in the liver's 

 secretions that we should find proofs of this dissociation of 

 corpuscular elements. Indeed, we have in bilirubin, a bile- 

 pigment derived from haemoglobin, direct evidence of this fact. 



The Hepatic Blood-pigments. We have already analyzed 

 (in the second chapter) the process through which various 

 blood-pigments are transformed one into another. We will 

 now only refer, therefore, to the features which suggest the 

 purposes of the spleno-hepatic functions as regards these 

 bodies. 



We ascertained that the changes undergone in the liver 

 represented but a portion of a cycle of which the intestines 

 were the starting-point, bilirubin (excepting that transformed 

 into urobilin and stercorin) being reabsorbed from the intes- 

 tine and again used in the building up of haemoglobin. Ex- 

 perimental evidence was adduced to show (Macallum) that in 

 an animal fed on albuminate of iron free leucocytes crowded 

 with iron-pigment could be traced in transit through the in- 

 testinal mucous membrane in the villi, and that similar leu- 

 cocytes had been found in the spleen and in the liver. But 

 can we conclude from this that the iron-laden leucocytes find 

 their way to the spleen and that this organ constitutes a part 

 of the cycle? The anatomical relations of the structures in- 

 volved show that, even if such an arrangement did exist, it 

 could serve no useful purpose, since the leucocytes would but 

 penetrate the splenic structures to again enter the portal cir- 

 culation. Obviously, the only pathway available anatomically 

 is the venous one, since Macallum found the "leucocytes 

 crowded with granules of iron-pigments" in the venules of the 

 villi. 



The single venous channel at our disposal, therefore, is 

 that of the distribution of the villi, the ileum and jejunum 

 mainly, i.e., the superior mesenteric veins, which again lead 

 us to the portal vein. This probably means that the iron thus 

 taken from the intestine is not ready for the circulation, and 



