PATHOLOGICAL METABOLISM OF THE BLOOD 561 



Methods for the Determination of the Rate of Hemoglobin Destruc- 

 tion. In the paragraphs on tests of bone-marrow activity, it was pointed 

 out that the red blood-cell count depends, for the most part, upon the rel- 

 ative rate of blood formation and blood destruction. Even when blood 

 ' formation is going on rapidly, the total count may be low because of rapid 

 destruction of red cells, or the count may rise rapidly without any stimula- 

 tion of the blood-forming organs due to diminished red cell destruction. It 

 is therefore desirable to obtain more exact knowledge concerning the degree 

 and rate of erythrogenesis and hemolysis by more reliable criteria. This 

 is of particular importance in such diseases as p'ernicious anemia and 

 hemolytic icterus where it is of value to determine the effect of such 

 therapeutic measures as splenectcmy and transfusion upon the rate of 

 blood destruction and regeneration. 



Whereas the methods for the study of the rate of blood regeneration 

 are largely qualitative, there are fairly accurate indirect ways of esti- 

 mating the extent of blood destruction. Of these, two methods only merit 

 consideration: first, the estimation of the amount of urobilin excreted 

 in the urine and f eces ; and second, the determination of the tolerance to 

 injections of hemoglobin. 



The generally accepted view of the origin of urobilin is based upon the 

 assumption of a circulation of bile-pigments. According to this con- 

 ception, the bile-pigments are changed to urobilin by the reducing bac- 

 teria in the intestine. The urobilin thus formed is in part excreted in 

 the stools, in part destroyed, and in part resorbed by the portal blood 

 stream and returned to the liver. Should excessive hemolysis occur there 

 will be an increased excretion of bile-pigments by the liver and a cor- 

 responding increase in the amount of urobilin formed in the intestine. 

 Much of this excessive urobilin leaves the body in the stools, but inasmuch 

 as a large amount is also absorbed Vy the portal capillaries, an unusual 

 strain is thrown upon the hepatic mechanism which serves to remove this 

 from the blood. Not infrequently, therefore, considerable urobilin escapes 

 into the general circulation and is excreted by the kidneys. Urobilinuria 

 may then occur in conditions of increased hemolysis; but it may be 

 found also in conditions unassociated with evidences of hemoglobin dis- 

 integration. In such instances, it must be assumed, urobilinuria results 

 from an overflow through a poorly functioning liver in which there is inter- 

 ference with the normal function of removing urobilin from the blood. It 

 is because urobilinuria may occur in conditions other than those associated 

 with excessive blood destruction, that emphasis has been placed on the 

 examination of the stool as well as the urine. 



Although an unusual degree of blood destruction results in a greatly 

 augmented quantity of urobilin in the stool, there is no absolute quanti- 

 tati re relationship between the actual amount of urobilin formed and the 

 amount of blood destroyed. There are two reasons for this : first, the pro- 



