DIGESTION. 229 



cells alone; and a third variety are lined equally with each kind of cell. 

 (3) In the muco-salivary or mixed glands, as the human submaxillary 

 gland, part of the gland presents the structure of the mucous gland, 

 whilst the remainder has that of the salivary glands proper. 



Nerves and blood-vessels. Nerves of large size are found in the sali- 

 vary glands, they are contained in the connective tissue of the alveoli 

 principally, and in certain glands, especially in the dog, are provided with 

 ganglia. Some nerves have special endings in Pacinian corpuscles, some 

 supply the blood-vessels, and others, according to Pfliiger, penetrate the 

 basement membrane of the alveoli and enter the salivary cells. 



The blood-vessels form a dense capillary network around the ducts of 

 the alveoli, lUing carried in by the fibrous trabeculae between the alveoli, 

 in which also begin the lymphatics by lacunar spaces. 



Saliva. Saliva, as it commonly flows from the mouth, is mixed with 

 the secretion of the mucous glands, and often with air bubbles, which, 

 being retained by its viscidity, make it frothy. When obtained from the 

 parotid ducts, and free from mucus, saliva is a transparent watery fluid, 

 the specific gravity of which varies from 1004 to 1008, and in which, 

 when examined with the microscope, are found floating a number of min- 

 ute particles, derived from the secreting ducts and vesicles of the glands. 

 In the impure or mixed saliva are found, besides these particles, numer- 

 ous epithelial scales separated from the surface of the mucous membrane 

 of the mouth and tongue, and the so-called salivary corpuscles, discharged 

 probably from the mucous glands of the mouth and the tonsils, which, 

 when the saliva is collected in a deep vessel, and left at rest, subside in 

 the form of a white opaque matter, leaving the supernatant salivary fluid 

 transparent and colorless, or with a pale bluish-grey tint. In reaction, 

 the saliva, when first secreted, appears to be always alkaline. During fast- 

 ing, the saliva, although secreted alkaline, shortly becomes neutral; and 

 it does so especially when secreted slowly and allowed to mix with the 

 acid mucus of the mouth, by which its alkaline reaction is neutralized. 



Chemical Composition of Mixed Saliva (Frerichs). 



Water 994-10 



Solids 5-90 



Ptyalin .1-41 



Fat 0.07 



Epithelium and Proteids (including Serum-Al- 

 bumin, Globulin, Mucin, &c.) . . . 2.13 

 Salts Potassium Sulpho-Cyanate 



Sodium Phosphate .... 

 Calcium Phosphate .... 

 Magnesium Phosphate 

 Sodium Chloride .... 

 Potassium Chloride 



2-29 



5-90 



