344 CONSIDERATION OF CARBON COMPOUNDS. 



others as mixtures of leucine, C 6 H 13 NO 2 , tyrosim, C 9 H n NO 3r 

 asparaginic acid, etc. 



Haemoglobin (Hemalocrystalline). This substance is the coloring 

 agent of the blood ; it resembles the proteids in many respects, 

 but differs from them in being crjstallizable and in containing 

 iron. Its composition has been found to correspond to the 

 formula C 600 H 960 154 179 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 another gas, carbon dioxide 

 for instance, is passed through it, the latter gas causing the 

 bright red color to change into a dark red. Upon this absorp- 

 tion and exchange of the two gases in the haemogloblin depend 

 its action in the blood, where it exists in the red blood-corpus- 

 cles. Arterial blood is bright red, and contains oxy haemoglobin r 

 haemoglobin loaded with oxygen; this latter element is ex- 

 changed by the blood during its passage through the system for 

 carbon dioxide, produced by the oxidation of the various organic 

 substances, and the dark venous blood, now loaded with carbon 

 dioxide, returns to the lungs, where the carbon dioxide is again 

 exchanged for oxygen. 



Haemoglobin absorbs certain other gases, for instance, carbonic 

 oxide, nitrogen dioxide, and hydrocyanic acid more readily than 

 either oxygen or carbon dioxide, and the poisonous properties 

 of these gases are due to their rendering haemoglobin incapable 

 of taking up oxygen. 



Haemoglobin may be obtained in beautiful red crystals, which 

 diifer somewhat in shape and solubility in water according to- 

 the species of animal from whose blood they were obtained. 



Haemoglobin may be decomposed by boiling with alcohol (or 

 by other agents) into albumin and a substance called hcematin, 

 C 34 H 34 N 4 5 Fe, which is soluble in acidified alcohol. Haematin is 

 a bluish-black powder, which forms with hydrochloric acid a 

 crystalline compound, which fact is made use of as a charac- 

 teristic microscopical test for the presence of blood. 



Animal cryptolites. This term is applied to a number of 

 animal substances of an unknown composition, but resembling 



