I0 6 NORMAL HISTOLOGY. 



shaped or of a horseshoe form. The protoplasm resembles that ( 

 the large mononuclear cells, presenting ordinarily no granularity, 

 few eosinophile granules, however, sometimes being distinguishabl 



4. Polymorphonuclear leucocytes constitute the form mo< 

 frequently encountered, and probably represent the fully develope 

 condition of the leucocyte. These elements are distinguished b 

 the variously distorted nucleus, which, being fairly rich in chrc 

 matin, presents a striking figure in stained preparations. Th 

 segments usually retain connection by delicate threads of chromatin 

 exceptionally the bridges become broken, in which case the ten 

 ' ' polynuclear' ' is appropriate. Occasionally cells may be observe 

 containing granules which stain deeply with eosin. Such * ' eosinx 

 philic' * leucocytes probably represent later phases of developmen 

 According to Ehrlich's teaching, the lymphocytes and the leuc< 

 cytes are to be regarded as distinct varieties of cells, the former bein 

 derived from lymphoid tissues and thelatter from bone-marrow. 



Ehrlich has classified the granules occurring within the leucocyte 

 into the following four groups, according to their affinity for "acid, 

 ' * basic, " or " neutral' ' stains : 



1. a-granules, which are coarse and highly refracting, appearin 

 fresh blood as minute fat particles. These granules possess 



strong affinity for eosin and acid stains ; hence they are known i 

 ^eosinophile and oxyphile. " 



2. y-granules, which are coarse, intensely basophilic, and occur i 

 the mononuclear c ' mast' ' cells. 



3. S-granules, which are fine, basophilic, and are seen in the pob 

 morphonuclear leucocytes. 



4. s-granules, which exhibit an affinity for neutral staining mi: 

 tures and are neutrophilic. These constitute the most abundant ar 

 important variety of granules in the polymorphonuclear cells. 



THE COLORED CELLS OF THE BLOOD. 



The adult mammalian red blood-cell represents a condition c 

 .^^trogresslon, since in its development it has suffered the loss of i 

 nucleus and a profound metamorphosis of its protoplasm, chang< 

 of such importance that some authorities dispute the propriety c 

 regarding the mammalian red blood-corpuscles as true cells. T\ 

 presence or absence of the nucleus within the colored corpuscL 

 together with its general form, furnishes a basis for a division of a 

 vertebrate bloods into 



A. Those having nucleated, oval red corpuscles : includin 

 fishes (except cyclostomata, which have round, discoidal cells, as tf 

 lamprey), amphibians, reptiles, and birds. 



B. Those having non-nucleated, round, discoidal red coi 



