76 THE STRUCTURE AND LIFE OF BIRDS chap. 



them. These are called Amoebae from their incessant 

 restlessness. At one moment they may be round, 

 the next they throw out a limb on one side, the next 

 that limb is withdrawn and another thrown out else- 

 where. Wherever food comes in contact with them 

 they make a mouth and swallow it. The colourless 

 corpuscle is one of these simplest of creatures, lead- 

 ing a life of its own within the blood-vessels, but 

 dependent on the body for the conditions which make 

 life possible to it. There are several forms of 

 them, and some, it is believed, do us the priceless 

 service of swallowing the germs of diseases that find 

 their way into the blood. The bacillus that has 

 survived immersion in the strong acid juices of the 

 stomach is killed, so it is believed, by these small and 

 half independent organisms. Whether this is so or 

 not, it is certain that when the blood is thick with 

 corpuscles, red and white, there is less liability to 

 disease. 



The red corpuscles carry a great deal of oxygen, 

 and thus they are able to oxidise the tissues, i.e. burn 

 them, for ordinary burning is only a rapid process of 

 oxidation. If the supply of oxygen is cut off from 

 it, a fire at once goes out. The oxygen in the blood 

 keeps up the warmth of the body by slowly burning it. 

 And in birds, with their very high temperature, the 

 process is more rapid than in other warm-blooded 

 animals. The redness of arterial blood is due entirely 

 to the pigment haemoglobin in the red corpuscles. 

 When they lose their oxygen it can be proved by 

 experiment that they become black, the colour of 

 venous blood. 



