156 ANIMAL LIFE 



In this quest we soon meet with success. The 

 red colouring matter of blood is such a vivifying 

 substance. The aerating virtue of the blood lies in 

 that colour, and should it fade we become weak and 

 anaemic ; should it disappear, we succumb ; our fires 

 burn out from need of the oxygen which the red 

 pigment, and it alone, can dispense. 



To most animals, as to ourselves, this pigment is 

 essential. All the members of the vertebrate class, 

 cold- as well as warm-blooded, possess it. It gives not 

 only the colour to the blood, but the dark tint to the 

 muscles. Below this class it occurs sporadically in 

 snail, starfish, and worm, conferring upon their blood 

 and muscles a greater efficiency than is possessed by 

 their colourless relatives, and the ability to thrive in 

 stagnant water or amid ill-ventilated surroundings. 



In producing the gross colour of the animal this 

 pigment takes but a small share, and it is only when 

 a given supply has done its work and steps aside to 

 make room for the new flow that comes from the 

 marrow of the bones that it is apparently removed 

 from the blood-vessels, transported to the skin, con- 

 verted into a black pigment, and stored in hair and 

 feathers, there to give rise to the colour of the body. 



But the interest of the red blood-pigment is not 

 confined to its wide distribution, its life-giving property, 

 or its usefulness as a source of surface colouring. In 

 its chemical nature this pigment shows a family con- 

 nection with the green colouring matter of plants. 

 In their purest known state each of these bodies, 



