124 NORMAL HISTOLOGY. 



haemoglobin they contain, which is said to constitute 90 per cent, of 

 their solid matter. It is readily oxidized and reduced again, and 

 serves to carry the oxygen of the air, obtained during the passage 

 of the blood through the pulmonary capillaries, to all parts of 

 the body. The red corpuscles, therefore, subserve the respiratory 

 function of the blood, as the plasma subserves its nutritive func- 

 tion. 



The leucocytes, or white blood-corpuscles, are cellular elements 

 closely resembling the amoeba in their structure, which are present 

 in the blood in much smaller number than the red corpuscles, the 

 usual proportion being about one to six hundred. They vary some- 

 what in size and structure, either because of differences in their origin, 

 or because they are in different stages of development. The majority 

 of them are capable of ameboid movements ; but while they are cir- 

 culating in the more rapid currents of the blood the constant shocks 

 they receive through contact with other corpuscles or with the vascu- 

 lar walls keep their cytoplasm in a contracted state and they maintain 

 a globular form. If, however, through any chance they remain for 

 some time in contact with the wall of a vessel, they are able to make 

 their way between the endothelial cells and pass out of the circulation 

 into the surrounding tissues. Here they creep about, and for this rea- 

 son have been called the migratory or wandering cells of the tissues. 

 They ultimately either suffer degenerative changes and disappear, 

 or find their way back into the circulation through the lymphatic 

 channels. During these excursions they may incorporate stray 

 particles in the tissues, and thus act as scavengers. This activity 

 has been called their phagocytic function, and may play an impor- 

 tant part in the removal of material that should be absorbed or of 

 particles that would otherwise be injurious to the tissues ; e. g., 

 bacteria. (See statements regarding the nature of colostrum-cor- 

 puscles.) 



The emigration of leucocytes from the bloodvessels is pronounced 

 in many of the inflammatory processes, and their phagocytic func- 

 tion may have a marked influence on the result. 



The leucocytes are produced in the lymphadenoid tissues of the 

 body, the lymphatic glands, thy m us, spleen, and the more diffusely 

 arranged tissues of like structure, but probably most abundantly in 

 the red marrow of the bones. 



A close study of the leucocytes has resulted in their subdivision 

 into a number of groups according to their morphological differences 



