BLOOD PIGMENTS 



477 



The liematiu is, tlierofore, presumably acid, and tlie coiiipound pro- 

 tein, hemoglobin, is somewhat like the nucleoproteins in nature. Hem- 

 oglobin ordinarily does not crystallize readily, especially the hemo- 

 globin of man, and it is doubtful if it ever does so in the living 

 tissues, although possibly this may occur in the center of large hema- 

 tomas. In bodies that have undergone postmortem decomposition, 

 and occasionally in specimens kept for microscopic purposes, irregu- 

 lar orange-yellow crystalline masses of hemoglobin may be found. 

 Tliis occurs particularly if the blood has been acted upon by hemo- 

 lytic agents or has undergone i)utrefactive changes, and then is 

 hardened in alcohol. The crystals are either oxyhemoglobin, or more 

 often an isomeric or polymeric modification, parahemoglohin (Nen- 

 cki). Hemoglobin also enters cells unchanged, imparting a dififuse 

 yellowish color, and apparently it is non-toxic.'*"'^ If present in the 

 blood in large enough amounts it is excreted unchanged in the urine, 

 but at least one-sixtieth of the total number of red corpuscles must 

 be in solution at one time to produce hemoglobinuria; in man at 

 least 17 e.c of laked corpuscles must be injected to accomplish this.'*''' 



Addis *'" has developed the following conception of the metabolism 

 of hemoglobin. Free hemoglobin, liberated, especially by the phago- 

 cytes of the spleen, is taken up by the other phagocytes, notably the 

 Kupffer cells of the liver, which pass it on to the liver cells. The 

 ])igment moiety, hemochromogen, is separated from the globin, and 

 converted through removal of its iron into hiliruhin. The bilirubin 

 excreted into the intestine is there reduced to urobilinogen, w'hich is 

 in part reabsorbed and polymerized into uroMlin, which in turn- is 

 possibly polymerized into a larger complex. In the liver this uro- 

 bilin complex has restored to its pyrrol nuclei the original side chains, 

 and then is used to form new hemoglobin molecules. This hypoth- 

 esis is merely tentative, but it affords a useful "working hypoth- 

 esis" for the consideration of many phases of pigment metabolism. 



In the decomposition of hemoglobin the first step is the splitting 

 of the globin (which does not form pigments) from the hematin, from 

 which many pigments may be derived. 



Hematin. — The formula given for this substance by Neneki,. 

 C.^nHooN^Fe04, has been generally accepted, although it is not cer- 

 tain that the hematin of all animals is the same. It is found fre- 

 quently as an amorphous, dark-brown or bluish-black substance, in 

 large, old extravasations of blood, but seldom in small hemorrhages. 

 As a pathological pigment, however, hematin is by no means so fre- 

 quently found as its derivatives. Schumm ^^ observed a patient with 

 chromium poisoning wdio showed for several days abundant hematin 

 free in the blood. He has also found it in malaria, pernicious anemia 



4TaBarratt and Yorke, Brit. Med. Jour., Jan. .31, 1914. 



47bSellards and IMinot, Jour. Med. Res., 1916 (34), 4G9. 



4Tcj\rch. Int. Med.. 1913 (1.5), 412. 



48Zeit. phvsiol. Chem., 1912 (80), 1; 191.3 (87). 171; 1916 (97), 32. 



