THE WHITE BLOOD-CORPUSCLES 815 



meal. They vary from one in 300 to one in 600 red corpuscles, or, taken 

 as a whole, from 18,000 to 9000 per cubic millimetre of blood. 



FORMATION OF THE LEUCOCYTES 



In classifying the white corpuscles of the blood it is essential to know 

 whether the different varieties we have described represent phases in one 

 and the same corpuscle or a number of different cells of separate origin. 

 The question as to the specificity of each kind of leucocyte cannot be 

 regarded as settled. According to some observers, Gulland and others, 

 all the leucocytes are derived from one kind of cell, namely, the lymphocyte. 

 Ehrlich and his school, on the other hand, regard each type as forming a 

 tissue sui generis, originating in separate localities and from distinct kinds of 

 cells. Since division of the leucocytes in the blood itself appears to be an 

 occurrence of the utmost rarity, we must locate the original seat of forma- 

 tion of these cells in two tissues. Lymphocytes are derived from the 

 adenoid tissue forming the lymphatic glands and the lymph nodules sur- 

 rounding so many of the mucous cavities. These lymphatic nodules 

 present towards their centre a clearer zone, consisting of cells rather larger 

 than those of the periphery and known as the ' germ centre.' The nuclei 

 in these cells present a well-marked reticular arrangement, and nuclear 

 figures are often to be seen. By the division of these cells lymphocytes 

 are formed, pushing towards the periphery of the nodule, where they make 

 their way into the lymph- sinus and are carried slowly by the lymph into 

 the blood. Some of these lymphocytes may possibly pass directly through 

 the capillary wall into the blood-stream. 



The other tissue concerned in the formation of leucocytes is the bone- 

 marrow. This is the chief blood-forming tissue of the body, since it is re- 

 sponsible also for the production of all red blood-corpuscles which are formed 

 during adult life. In the red marrow are seen a number of cells known 

 as myelocytes. These contain a single rounded nucleus and a well-marked 

 protoplasm which may be non- granular or may contain granules, generally 

 eosinophile in character, but sometimes basophile. It is stated that all 

 intermediate stages are to be found in the bone-marrow between these 

 ' myelocytes ' and the polymorphonuclear leucocyte as well as the eosinO' 

 phile leucocyte. It is certain that in the disease leukaemia, which is 

 associated with an increased number of leucocytes in the blood, there may 

 be an increase either of eosinophile cells or of the neutrophile cells, and 

 either condition is associated with changes in the red bone- marrow. We 

 may therefore provisionally arrange the leucocytes of the blood according 

 to their origin as follows : 



(1) Small lymphocyte derived from lymph oid tissue. 



(2) Large mononuclear or hyaline corpuscle : doubtful whether derived 

 by a growth of (1) or from a myelocyte. 



(3) Polymorphonuclear leucocyte formed in bone-marrow. 



(4) Eosinophile cell derived from similar cells in the bone- marrow. 

 This origin of the eosinophile corpuscle is rendered more probable by the 



