STRUCTURE OF THE VERTEBRATES 



247 



into several distinct nuclei. They are ameboid in appearance and 

 are actively phagocytic (that is, they ingest foreign particles). 

 These cells form about seventy-four per cent of all leucocytes 

 in the human. The great majority show a neutral staining 

 reaction, but a few take an acid stain. The granulocytes are 

 classified according to their staining reactions, and the size of 

 the granules. 



A- Lymphocyte 



C. Neutiophile 



B. Mononuclear 





D. Mast E. Acidophile M^ 



F. Platelets 



Fig. 137. Mammalian Leucocytes and Blood Platelets. 



The proportion of leucocyte types is of clinical value, since the 

 blood count indicates different physiological conditions. Most of 

 the white cells are phagocytic, and therefore have a definite func- 

 tion in preventing infections. Pus is made of dead white cells 

 and serum. In the human there are approximately 8,000 leuco- 

 cytes in each cubic millimeter of blood. 



Erythrocytes. The red cells contain haemoglobin which has 

 a strong affinity for oxygen, the combination of the two being 

 an unstable chemical compound. Due to this instability the 

 oxygen is liberated in the capillaries and passed to the tissues. 

 Internal respiration depends upon the amount of oxygen carried 

 to the cells, and insufficient oxvgenation may be caused either 



