444 BLOOD AND LYMPH. 



cent. Eosinophilic leucocytes form a subgroup of this variety. 'Itiey 

 have a similar segmented nucleus, but the cytoplasm contains nu- 

 merous coarse granules that stain in acid dyes, such as eosin, whence 

 the name. 



VP) Mast cells. These peculiar cells exist in very small numbers under 

 normal conditions, less than 1 per cent, of the total number of 

 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. 



Current opinions vary greatly in regard to the origin and 

 relations of these different forms of white blood-corpuscles, almost 

 every writer proposing some special hypothesis to indicate his 

 particular point of view.* In general, however, it may be said 

 that the divergent views fall under two heads. First, the so- 

 called dualistic theory, according to which there are two sources 

 of origin for these cells, namely, the lymphoblasts of the lymph 

 nodes which give rise to the small lymphocytes and the myeloblasts 

 of the bone-marrow, which give rise to the granular leucocytes of 

 the blood and probably also seive as the parent form for the large 

 mononuclear leucocytes and transitional forms. Second, the 

 Unitarian or monophyletic theory, according to which all the white 

 blood-corpuscles arise from a single form or variety of parent cells 

 that has the characteristics of a large or small lymphocyte. 

 Most authors perhaps believe that the various forms as they exist 

 in the blood are from an anatomical standpoint permanently 

 differentiated. Such a view implies, on the physiological side, that 

 each form has some special functional activity of its own. Little 

 or no progress has been made, however, in discovering the specific 

 physiology of the various 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 



* See Weidenreich for summary, "Ergebnisse der Anatomic und Entwickel- 

 ungsgeschichte," vol. 19, part n (1909), 1911. 



