ANIMAL FLUIDS AND TISSUES. 657 



Mdhcrmogtobin is a transformation-product of oxyhsemoglobin found 

 in sanguinous transudates and cystic fluids ; it also occurs in the urine 

 during haematuria and haemoglobin uria; and in the blood and urine 

 after poisoning with potassium chlorate, amyl nitrite, alkali nitrates, 

 and several other bodies. 



Hcemochromogen. When haemoglobin is acted upon by acids, alka- 

 lies, etc., it is split into globin (a histone) and hsemochrornogen. The 

 latter forms only about ^V of the haemoglobin molecule, contains all 

 of the iron present, and consequently the group to which the oxygen 

 is attached when oxyhsemoglobin is formed. In the presence of 

 oxygen haemochromogen is rapidly converted into haematin. 



Ilcematin. Just as haemochromogen is split from haemoglobin, 

 haematin is derived from oxyhaemoglobin. It is a comparatively 

 simple substance, having the formula C 34 H 34 N 4 FeO 5 . It is found in 

 the feces after hemorrhage in the intestine, and also after a diet con- 

 sisting largely of red meats. Haematin has been found in urine after 

 poisoning with arsenetted hydrogen. Haematoporphyrin (^H^N^Oj 

 is obtained when haematin is hydrolyzed. 



Haematoporphyrin occurs in traces in normal urine ; it is found in 

 greater quantity in urine after the use of sulphonal. Haematopor- 

 phyrin is isomeric with the bile-pigment bilirubin, and a pigment 

 closely resembling urobilin has been obtained by the action of reduc- 

 ing agents on haematoporphyrin. It is noteworthy that this substance 

 does not contain iron. 



Carbon monoxide haemoglobin is a molecular combination of one 

 molecule of haemoglobin and one molecule of carbon monoxide. The 

 combination is stronger than that between oxygen and haemoglobin and 

 this explains the poisonous action of carbon monoxide, which causes 

 death by replacing the oxygen of the blood. A similar and even 

 more stable chemical combination is formed with haemoglobin by 

 nitric oxide. 



Carbon dioxide haemoglobin (carbo-hwmoglobin). Haemoglobin has 

 the property of forming an unstable compound with carbon dioxide, 

 the CO 2 is, however, not attached to the same portion of the molecule 

 as that to which the oxygen (in oxy haemoglobin) is attached. Thus, 

 the presence of carbon dioxide does not prevent the absorption of 

 oxygen by haemoglobin, which is in great contrast to the action of 

 carbon monoxide, and is important in the process of respiration. 



Spectroscopic examination. The different haemoglobins are distinguished 

 chiefly by their absorption -spectra. In the following description the violet end 

 of the spectrum is assumed to be on the observer's right. 

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