GENERAL PROPERTIES! THE CORPUSCLES. 405 



white corpuscles. They have a polymorphic nucleus like the pre- 

 ceding group, but differ in the fact that the granules in the cyto- 

 plasm are strongly basophilic, that is, will stain only with basic 

 dyes, such as thionin. 



According to most of the authors who have studied the ap- 

 pearance and variation in number of these cells under pathological 

 conditions, the small lymphocytes are cells that have an origin and 

 function different from those of the granular leucocytes. While 

 the latter are supposed to originate from cells (leucoblasts, my- 

 elocytes) in the bone marrow, the lymphocytes are produced in the 

 nodules of the lymph glands and lymphoid tissue, and enter the 

 blood through the lymph circulation. Another view maintained 

 by some authors is that the various white corpuscles in the blood 

 represent different stages of development. According to this view, 

 the small lymphocytes as received from the lymph circulation are 

 the young or immature form, and they develop, while in the circu- 

 lation, through the stages represented by the large lymphocytes 

 and the mononuclear leucocytes to the mature form, the poly- 

 morphonuclear leucocytes. 



Variations in Number. Under -normal conditions the total 

 number of leucocytes may show considerable variation; the aver- 

 age number in health varies usually between 5000 and 7000 

 per cubic millimeter. A distinct increase in number is designated 

 as a condition of leucocytosis, a marked diminution as a condition of 

 leucopenia. Leucocytosis occurs under various normal conditions, 

 such as digestion, exercise or cold baths, pregnancy, etc. The 

 variations, relative or absolute, under pathological conditions, have 

 been studied with exhaustive care as an aid to diagnosis and classi- 

 fication. 



Functions of the Leucocytes. Perhaps the most striking 

 property of the leucocytes as a class is their power of making 

 ameboid movements, a characteristic which has gained for them 

 the sobriquet of " wandering" cells. By virtue of this property 

 some of them are able to migrate through the walls of blood capil- 

 laries into the surrounding tissues. This process of migration takes 

 place normally, but is vastly accelerated under pathological con- 

 ditions. As to the function or functions fulfilled by the leucocytes, 

 numerous suggestions have been made, some of which may be 

 stated in brief form as follows: (1) They protect the body from 

 pathogenic bacteria. In explanation of this action it has been 

 suggested that they may either ingest the bacteria, and thus destroy 

 them directly, or they may form certain substances, defensive 

 proteids, that destroy the bacteria. Leucocytes that act by ingest- 

 ing the bacteria are spoken of as " phagocytes" (ydyeiv, to eat; 

 cell). This theory of their function is usually designated as 



