354 THE BLOOD. 



lizable, and may be obtained in this form by treating a concentrated 

 solution of oxy haemoglobin with a saturated solution of potassium 

 ferricyanide until the color has changed to a port-brown. The 

 mixture is cooled to C., and treated with one-quarter of its 

 volume of cooled alcohol. When kept in the refrigerator crystal- 

 lization takes place in the course of a few days. The crystals are 

 of a brown color, and occur as needles, prisms, or hexagonal plate- 

 lets. They may be purified by recry stall ization from water in the 

 presence of alcohol. An aqueous solution of the substance is 

 brown, while its alkaline solutions are beautifully red. On exposure 

 to sunlight its neutral and dilute solutions gradually assume a 

 dark-red color, which is thought to be referable to a transformation 

 of methemoglobin into photomethcemoglobin. On spectroscopic 

 examination such solutions show one broad band of absorption in 

 the green portion of the spectrum no matter whether the reaction is 

 alkaline, neutral, or acid. Methaemoglobin proper under the same 

 conditions gives a fairly broad band of absorption between C and D, 

 nearer C, which is characteristic, and disappears on the addition of 

 sodium hydrate solution. In addition, two different bands may at 

 times be seen between D and E, which are thought to be referable, 

 however, to a contamination of the substance with hemoglobin. 

 Some observers further speak of an additional band near F, but 

 this is not characteristic. On reduction of the alkalinized solution 

 with ammonium sulphide the spectrum of hemochromogen results. 



According to v. Zeynek, photomethcemoglobin is in reality cyan- 

 haemoglobin, and is formed through the action upon the hemoglobin 

 of hydrocyanic acid which results from the ferricyanide in conse- 

 quence of the effect of sunlight. Pure methemoglobin is not 

 aifected by sunlight. 



Like oxy hemoglobin, methemoglobin is capable of combining 

 with certain gases to form molecular compounds. Of these, a 

 carbon dioxide methcemoglobin, a methcemoglobin sulphide, and a cyan- 

 methcemoglobin have been described. 



Hsematoporphyrin. This substance results from hematin when 

 this is treated with concentrated sulphuric acid saturated with 

 hydrobrornic acid : 



C 32 H 32 N 4 Fe0 4 + 2H 2 + 2HBr = 2C 16 H 18 N 2 O 3 + FeBr 2 + 2H 

 Hsematin. Hsematoporphyrin. 



During this process the iron of the hematin is split off, and a new 

 pigment, hsematoporphyrin, is formed. In the circulating blood of 

 vertebrate animals it is not found under normal conditions, but is 

 apparently formed in certain diseases, and during the long-continued 

 administration of sulphonal and related bodies, as also in lead- 

 poisoning and following intestinal hemorrhages, when it may also 

 be found in the urine. Among invertebrates it is said to occur in 

 the integument of the star-fish, in certain snails, in the earth-worm, 

 in various sponges, etc. 



