HOEMOGLOBIN. 261 



Oxyh&moglobin is readily obtained in crystals of a bright red 

 colour and soluble in water. It appears to act as a weak acid. 

 A dilute solution shows a characteristic absorption spectrum, 

 containing two chief dark bands, one on the Fraunhofer line D 

 and the other near E. 



By the action of reducing agents (e.g., ammoniacal ferrous 

 tartrate), or by the passage of an indifferent gas, or even by 

 exposure in a vacuum, oxyhaamoglobin is deprived of oxygen 

 and hemoglobin is produced. This is darker and more purple 

 in colour and more soluble in water. It readily absorbs oxygen 

 again from the air. 



By the decomposition of haemoglobin a colouring substance 

 named hamochromogen is obtained, which, by oxidation, be- 

 comes hcematin. This last substance is said to have the coin- 

 position C^HagN^eOg, and is a dark brown or black solid 

 insoluble in water, acids, alcohol, or ether, but easily soluble in 

 alkalies. By concentrated sulphuric acid, haematin is converted, 

 with removal of iron, into a purple red substance known as 

 h&mato-porphyrin, said to be C 16 H 18 N 2 3 . 



In addition to the red corpuscles, blood contains colourless 

 corpuscles or leucocytes. These are of lower specific gravity 

 than the red corpuscles, more variable in size and form, and 

 much less numerous, the relative numbers being one colourless 

 corpuscle to 300 or 500 red ones. They consist of fragments 

 of protoplasm and contain several albuminoids, glycogen or 

 animal starch, lecithin, and cholesterol. 



Blood plays an important part in the process of respiration. 

 It is through the blood that the animal organism receives the 

 oxygen so essential for the vital function. 



When blood is placed in vacuo gases are given off, their com- 

 position and amount varying considerably according to the 

 particular part of the body from which the sample was col- 

 lected. The following table represents the average gaseous 

 contents of arterial and venous blood. 100 volumes of blood 

 yield 



Arterial blood. Venous blood. 



Oxygen ... ... 20 8 to 12 



Nitrogen and argon ... 1 to 2 1 to 2 



Carbon dioxide 40 46 



