PRO TE IDS. 417 



colored red by iodine, violet or blue by iodine and dilute sulphuric 

 acid. It does not undergo putrefaction as readily as other proteids. 



Heemoglobin (Hcemato-crystallin, Hcemato-globulin). This substance 

 is the coloring agent of the blood ; it resembles the proteids in many 

 respects, but differs from them in being crystallizable and in con- 

 taining iron. Its composition has been found to correspond to the 

 formula C 600 H 960 N 154 O 179 FeS 3 . 



The most characteristic feature of a solution of haemoglobin is its 

 power of absorbing various gases ; it absorbs oxygen in considerable 

 quantities, thereby assuming a bright-red color, but gives up the 

 oxygen again when treated with deoxidizing agents. Accordingly, 

 we distinguish between common or reduced haemoglobin and oxy- 

 hsamoglobin ; by means of oxidizing and reducing agents, the one 

 body can readily be converted into the other. Solutions of oxy- 

 haemoglobin show a bright-red or scarlet color, those of haemoglobin 

 are much darker and of a purple tint. 



Upon the combination of oxygen with the haemoglobin of the 

 blood in the lungs, and the deoxidation of the haemoglobin by the 

 tissues, depends the process of respiration, which will be spoken of 

 later. 



Haemoglobin enters into combination with certain other gases for 

 instance, carbonic oxide, nitrogen dioxide, and hydrocyanic acid 

 more readily than with oxygen, and the poisonous properties of these 

 gases are due largely to their power of satisfying the affinities of 

 the haemoglobin, and in this way rendering it incapable of taking up 

 oxygen. 



Haemoglobin is soluble in water, in dilute solutions of albumin, of 

 the alkalies and their carbonates, and in sodium or ammonium phos- 

 phate. It is insoluble in strong alcohol, ether, and in the volatile 

 and fatty oils. With the spectroscope both oxyhaemoglobin and 

 reduced haemoglobin show characteristic absorption bands. 



Haemoglobin may be obtained in beautiful red crystals, which 

 differ in shape, and solubility in water, according to the species of 

 animal from whose blood they are obtained. 



Haemoglobin may be decomposed by boiling with alcohol (or by 

 other agents) into albumin and a substance called hcematin, C 34 H 35 

 ]S" 4 O 5 Fe, which is soluble in acidified alcohol. Haematin is a bluish- 

 black powder, which forms with hydrochloric acid a crystalline 

 compound, hcemine, which fact is made use of in a characteristic 

 microscopical test for the presence of blood. 



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