472 



SALIVA. 



[CH. XXX. 



plasm. The largest ducts have a wall of connective tissue outside 

 the basement-membrane, and a few unstriated muscular fibres. 



The secreting cells differ according to the substance they 

 secrete. In alveoli that secrete mucin (such as those in the dog's 



Pig. 394. Section of sub-maxillary gland of dog. Showing gland-cells, 6, and a duct, a, b, 

 in section. (Kolliker.) 



submaxillary, and some of the alveoli in the human submaxillary), 

 the cells after treatment with water or alcohol are clear and 

 swollen (fig. 395); this is the appearance they usually present in 



Fig- 395- Section through a mucous gland hardened in alcohol. The alveoli are lined 

 with transparent mucous cells, and outside these are the demilunes. (Heidenhain.) 



sections of the organ. But if examined in their natural state by 

 teasing a portion of the fresh gland in serum, they are seen to be 

 occupied by large granules composed of a substance known as 

 mucigen or mucinogen. When the gland is active, mucigeu is 

 transformed into mucin and discharged as a clear droplet of that 

 substance into the lumen of the alveolus. Outside these are 



