BLOOD AND HJEMOPOIETIC ORGANS 83 



varieties need not be described here, as they will be 

 found in any text-book, or, better still, can be learnt 

 from a personal study of stained films. We may deal, 

 however, with their place of origin and their function. 



White cells are the special product of two tissues in 

 the body (1) the red marrow of the bones, (2) the 

 adenoid tissue. 



The red marrow is confined within the narrow limits 

 of the short bones, the ribs, and the ends of the long 

 bones. Adenoid tissue, on the other hand, is diffused 

 throughout the body, existing partly in substantial 

 masses, such as the lymph glands, the thymus, the 

 tonsils, Peyer's patches in the intestine, and the Mal- 

 pighian bodies of the spleen, and partly in smaller 

 conglomerations to be found more or less in every tissue 

 and organ, probably including the bone marrow. It is 

 probable that the marrow is the sole seat of origin of the 

 granular cells, and that the adenoid tissue is the chief 

 breeding-ground of lymphocytes. Whether or not the 

 latter are also produced in the marrow, or, to put it 

 otherwise, whether or not the marrow, like other tissues, 

 also contains some adenoid tissue, is still disputed. In 

 lymphatic leukaemia the red marrow becomes virtually 

 converted into a mass of adenoid tissue, with the natural 

 result that the granular cells disappear almost entirely 

 from the blood. Whether such a replacement of the 

 normal marrow is to be regarded as an invasion by 

 lymphocytes or a mere hypertrophy of already existing 

 adenoid tissue depends upon the view one takes as to 

 whether or not lymphocytes are a natural product of 

 the marrow. 



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