858 PHYSIOLOGY 



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 surrounding 

 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 

 responsible 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 

 eosinophile 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 neutrophile cells, and 

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

 may therefore provisionally arrange the leucocytes of the blood accord! jiu 

 to their origin as follows : 



(1) Small lymphocyte derived from lymphoid 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 



