76 THE STRUCTURE AND LIFE OF BIRDS cyap, 
them. These are called Amcebz 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that limb is withdrawn and another thrown out else- 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, ze, 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 hzmoglobin in the red corpuscles. 
When they lose their oxygen it can be proved by 
experiment that they become black, the colour of 
venous blood. 
