142 



FUNCTIONS OF NUTRITION. 



rounded with a delicate layer of connective tissue, in which are dis- 

 tributed the capillary blood-vessels, supplying the materials for secre- 

 tion. 



FIG. 22. 



SECTION OF THE SUBMAXILLAKY GLAND FROM THE DOG. a. Salivary duct, with cylindrical epithe- 

 lium and central cavity. 6. Follicle, with glandular epithelium and central cavity. (Kolliker.) 



FIG. 23. 



Physical Properties and Composition of the Saliva. Human saliva, 

 from the cavity of the mouth, is a colorless, slightly viscid, alkaline 

 fluid, with a specific gravity of 1.005. When first discharged, it is 

 frothy and opaline, holding in suspension minute flocculi. After stand- 

 ing for some hours in a cylin- 

 drical vessel, an opaque, whitish 

 deposit collects at the bottom, 

 while the supernatant fluid be- 

 comes clear. This deposit (Fig. 

 23), consists of epithelium scales 

 from the internal surface of the 

 mouth, detached by mechanical 

 attrition, minute, roundish, gran- 

 ular, nucleated cells, apparently 

 epithelium from the mucous fol- 

 licles, some granular matter, and 

 a few oil-globules. The super- 



natant fluid has a faint bluish 

 tinge, and becomes slightly opa- 

 lescent by boiling or by the addi- 

 tion of nitric acid. Alcohol in 

 excess causes the precipitation 

 of abundant whitish flocculi. 

 According to the analyses of Bidder and Schmidt, the composition 

 of saliva is as follows : 



BUCCAL AND GLANDULAR EPITHELIUM., with Gran- 

 ular Matter and Oil-globules ; deposited as sedi- 

 ment from human saliva. 



