26 THE BLOOD. 



By what other name are they known? 

 Leucocytes. 



What is their proportion, numerically, to the red corpuscles ? 



The proportion is 1 to 500 or 600, but this relation is varied by 

 conditions of health and disease, by age, etc.. being more abun- 

 dant in youth, in anaemic conditions, in pregnancy, and after a full 

 meal. 



What power is peculiar to white corpuscles? 



The power of amoeboid movement, by which they are able to 

 pass through the walls of capillaries into the surrounding tissues. 

 This we call diapedesis. The physiological value of this is not 

 known. 



What is the source of the white corpuscles ? 



Leucocytes come, no doubt, from the lymph-glands, in which 

 they may be seen in large numbers " lymph-corpuscles " and 

 from which they are poured into the blood. They also originate 

 by fission. Some also, probably, are derived from the spleen and 

 from the thymus gland, perhaps also from microcytes. 



What is the ending of the leucocytes ? 



Many, probably, are decomposed in the blood-vessels, but more 

 end as colored cells ; still others take part in inflammatory pro- 

 cesses and are ended in this way. 



What are the uses of the blood ? 



(1) To receive and convey food and oxygen to all the parts of 

 the body. 



(2) To receive from the organs and carry away the refuse mat- 

 ters to other organs whose function is to excrete them. 



(3) To warm and moisten all parts of the body. 



What is tHe active ingredient of the blood in its oxygen-carry- 

 ing function? 



Haemoglobin. In the lungs the haemoglobin of the red corpus- 

 cles is combined in loose chemical union with oxygen, and this 

 union is broken down in the tissues of the body. 



What is the difference between arterial and venous blood? 



(1) Arterial blood is bright red (scarlet) from the combination 

 of haemoglobin with oxygen (oxy-haeinoglobin) ; and venous blood 

 is purplish or blue from deoxidation of the oxy-haemoglobin. 



(2) Arterial blood coagulates somewhat more quickly. 



