27 



The common leucocyte or polymorphonuclear cell has 

 nothing to do with the lymphocyte or lymph gland in its 

 development, but has two sources of origin, the first and most 

 important being the myelocyte, containing the fine eosinophil 

 granules. 



These myelocytes change in the marrow into the poly- 

 morphonuclear cells, and the marrow is, therefore, a reserve 

 store as well as factory of the polymorphonuclear cells, which 

 can be called on to supply a leucocytosis at a moment's notice. 



In normal conditions only the ripe or fully developed forms 

 of polymorphonuclear cells are found in the blood — the mono- 

 nuclear and transitional forms remaining in the marrow. 



The other and disputed source of the common leucocyte 

 is the large mononuclear cell. It is said that a small proportion 

 of the polymorphonuclears arise by transitional stages from this 

 hyaline cell. 



The coarsely granular eosinophil cells of the normal blood 

 are derived from the coarsely granular myelocyte. 



Looking at the matter broadly we have therefore the 

 lymphocytes arising in the lymph structures, and the ordinary 

 polymorphonuclear cells arising in the bone marrow. 



Having thus briefly described the character and origin of 

 the cells of the blood, let us turn to the question of the 

 variations, both in total number of white cells and also in the 

 relative proportion of the cells. 



Normally there are 7,000 to 10,000 leucocytes in the cubic 

 millimetre of blood, giving a proportion of one white to 500 or 

 600 red cells. 



If there is a definite increase of these cells the condition 

 is termed " leucocytosis ; " if a diminution, " leucopaenia " or 

 hypoleucocytosis. 



Where it happens that the leucocytosis is chiefly due to 

 an increase in the number of the lymphocytes, the term 

 lymphocytosis is employed. 



This fact of leucocytosis is one of the most interesting in 

 all haematology. From the time when Virchow first described 

 it up to the present numberless workers hvve been engaged 

 upon it. 



