2 54 



THE DEVELOPMENT OF THE VASCULAR SYSTEM 



and staining qualities of their cytoplasmic granules, the myelocytes give rise to 

 three types of granular leucocytes: 



i. Neutrophiles, or leucocytes with a finely granular cytoplasm which is 

 neutral in its staining reactions, coloring slightly with both acid and basic stains. 

 In development, their nuclei take up an eccentric position and become crescentic, 

 horse-shoe shaped, or in the older stages moniliform (three or four pieces linked 

 together). As it changes in form the nucleus undergoes pyknosis and stains in- 

 tensely. Neutrophiles are produced in the bone marrow of the embryo during 

 the fifth month. In the human adult they form 70 to 72 per cent, of the leuco- 

 cytes in normal circulation. 



2. Eosinophilcs, or coarsely granular leucocytes, are characterized by their 



large cytoplasmic granules 

 which stain intensely red 

 with eosin. In development 

 the nucleus becomes bilobed. 

 Eosinophiles form 2 to 4 per 

 cent, of the leucocytes in 

 normal human blood. 



/•''^Y.-?'' According to Weidenreich 



■-'-':'■'' ':• '' (Arch. f. mikr. Anat., vol. 82, pp. 



'■•:': '[^^'^''^fSzh 2S2-2S6), the eosinophilic gran- 



'.'■'■' '■■■•r^l^ ules are not endogenous but are 



fragments of red blood corpuscles 

 which have been ingested by the 

 leucocytes, or are formed from 

 hemoglobin derivatives. Bader- 

 scher (Amer. Jour. Anat., 1013, 

 vol. 15, pp. 69-86) finds in the vicinity of degenerating muscle fibers in salamanders numer- 

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

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

 (Anat. Record, vol. 8, p. 135, 1914) finds that the granules of eosinophilic myelocytes dif- 

 ferentiate from a non-granular cytoplasm. These basophilic granules become eosinophilic. 





Fig. 246. — Giant cell from the bone marrow of a kitten, 

 showing pseudopodia extending into a blood-vessel (]'), and 

 giving rise to blood-plates (bp) (J. H. Wright). 



3. Basophilcs, or Mast Leucocytes CMaximow), form only 0.5 per cent, of the 

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

 several pieces which stain intensely. The granules are variable in number, size 

 and form, and often stain so heavily as to obscure the nucleus. The cytoplasm 

 is clear and vacuolated. Basophiles have been regarded as degenerating granular 

 leucocytes but at present this view is not generally accepted. 



Origin of the Blood Plates. — In the bone marrow and spleen pulp are giatit 



