32 HISTOLOGY. 



neuroepithelial cell is to transmit this stimulus to the nerve fibres which 

 branch around its lower part. 



PROCESSES OF SECRETION. 



Many cells can elaborate and discharge certain substances which do 

 not become parts of the tissue. Such cells are called gland cells and their 

 products are either used in the body (secretions) or, being of no value, they 

 are removed (excretions). The processes of elaboration and discharge 

 of either secretion or excretion may often be recognized by changes in 

 the form and contents of the cell, indicating that it is empty or full of 

 secretion, as the case may be. A gland cell which is full of elaborated 

 secretion is called "active," and one in which the secretion is not apparent, 

 though it may be in process of formation, is called "resting." The 

 appearances of secretion differ in two types of gland cells, the serous, which 

 produce a watery secretion like that of the parotid salivary gland, and the 



^^" Granule. 

 Granule. 



,-- -_ ,..-,,,, ^ ^ Protoplasm. 



Protoplasm. 



New granule. 

 Basal filaments. 



Nucleus. 



%:W^_ 



Nucleolus. 



FIG. 34. Two SEROUS GLAND-CELLS FROM THE SUBMAXILLARY GLAND OF A GUINEA-PIG. X 1260. 



In cell B the granules have passed into the unstainable state; new stainable granules are beginning 



to develop in the protoplasm. 



mucous, which form a thick secretion such as occurs in the nose and 

 throat. 



The nucleus of empty gland cells often has a fine chromatin network 

 together with distinct nuclear granules. The granules are lacking when 

 the cell is full of secretion and the chromatin takes the form of coarse 

 fragments. Doubtless the granules pass from the nucleus into the proto- 

 plasm, but whether they become true secretion granules is uncertain, since 

 similar phenomena have been observed in nerve celis. .$ 



The protoplasm of serous gland cells at the beginning of secretion 

 exhibits distinct granules, coarser than microsomes, staining intensely 

 with certain dyes (Fig. 34, A). The granules enlarge, lose their staining 

 capacity, and are transformed into drops of secretion with which the cell 

 becomes charged. As a whole, the cell is larger and clearer than before. 



