148 HISTOLOGY. 



Cells containing coarse blue granules, which often obscure the nucleus, 

 are called mast cells. (The German word mast, meaning food, was applied 

 to them because of supposed nutritive functions.) They form about 

 0.5% of the leucocytes in the blood. Along the blood vessels, especially in 

 the mesentery, mast cells may be found in connective tissue if it is hardened 

 in alcohol and stained with a basic stain like methylene blue. Zenker's 

 fluid, a preservative often used, destroys these granules. (The mast cells 

 of connective tissue are larger than those in the blood, and generally have 

 rounded nuclei. They have been said to arise independently of the " mast 

 leucocytes.") 



Polymorphonuclear cells with coarse granules which stain red with 

 eosin, an acid stain, are called eosinophiles [oxyphiles, acidophiles]. They 

 form from 2 to 4% of the leucocytes in the blood, a proportion greatly 

 increased in certain diseases. Eosinophilic cells occurring in connective 

 tissue sometimes have round nuclei. It is questionable whether such 

 forms are derived from the eosinophiles which migrate from the vessels. 



The third type of granular cell, unlike the other kinds, contains fine 

 granules, and these stain purple or lilac by taking both stains to some extent. 

 They are called neutrophiles and form 70 to 72% of the leucocytes in the 

 blood. They are actively amoeboid and are the principal wandering cells 

 of the body, leaving the blood vessels more readily than other forms. 



The relation of the various leucocytes to one another has not yet been 

 determined. The first forms which appear in embryonic blood have 

 rounded nuclei and are perhaps intermediate between lymphocytes and 

 large mononuclear leucocytes. They resemble the young erythroblasts 

 from which they may be derived. Many authorities consider it probable 

 that there is a common origin for all the blood cells. Like the red cor- 

 puscles the leucocytes in the adult are produced in the meshes of reticular 

 tissue outside of the blood vessels; the lymphocytes chiefly in the lymph 

 glands, and the granular leucocytes chiefly in the red bone marrow where 

 the red corpuscles also develop. The lymphocytes appear in the circu- 

 lation before the granular leucocytes. An investigator (Engel) of the 

 blood in pig embryos found that well defined leucocytes similar to lympho- 

 cytes appeared first in pigs of 8 cms. Another investigator (Sabin) has 

 recorded that in the lymph glands of an 8 cm. pig the lymphocytes are first 

 recognizable. From these independent studies it seems that lymphocytes 

 appear in the lymph glands and in the blood at about the same time. 

 " In the guinea pig there seems to be a connection between the time of the 

 appearance of the polymorphonuclear leucocytes in the marrow and in 

 the blood" (Jolly and Acuna). The granular leucocytes appear in the 

 blood and in the marrow at "first as cells with round nuclei. Such cells 



