246 THE DEVELOPMENT OF THE VASCULAR SYSTEM 



premyelocytes. They give rise to myelocytes, cells with round or crescentic 

 nuclei and granular cytoplasm. Similar cells are developed in the lym- 

 phoid organs. By undergoing changes: (i) in the form and structure of 

 their nuclei, and (2) in the size and staining qualities of their cytoplasmic 

 granules, the myelocytes give rise to three types of granular leucocytes. 



i. Neutrophils (70 to 72 per cent of all leucocytes). These have a 

 finely granular cytoplasm which is neutral in its staining reactions, color- 

 ing by the interaction of both acid and basic stains. In development, their 



FIG. 253. Giant cell from the bone marrow of a kitten, showing pseudopodia extending into 

 a blood vessel (V), and giving rise to blood plates (bp) (Wright). 



nuclei take up an eccentric position and become, crescentic, horse-shoe 

 shaped, and, in the older stages, lobate. As it changes in form, the nucleus 

 undergoes pyknosis and stains intensely. 



2. Eosinophils (2 to 4 per cent of all leucocytes). These are charac- 

 terized by coarse cytoplasmic granules that stain intensely with acid dyes. 

 In development the nucleus becomes bilobed. 



It is commonly held that the eosinophilic granules differentiate endogenously (Dow- 

 ney, 1914). However, Weidenreich (1913) regards these granules as ingested fragments 

 of red corpuscles or their hemoglobin derivatives. Badertscher (1913) found numerous 

 eosinophils and free eosinophilic granules in the vicinity of degenerating muscle fibers in 

 salamanders. Also, during trichiniasis in man, when there is extensive degeneration of 

 muscle fibers, the number of eosiniphils in the blood becomes greatly increased. 



3. Basophils or Mast Leucocytes (0.5 per cent of all leucocytes). 

 Their nuclei are very irregular in form and may be broken down into 

 several pieces which stain intensely. The cytoplasmic granules are varia- 

 ble in number, size, and form, and often stain so heavily with basic dyes 

 as to obscure the nucleus. Basophiles have been regarded as degenerating 

 granular leucocytes, but at present this view is not generally accepted. 

 They are apparently distinct from the 'mast cells' of the tissues. 



