154 HUMAN PHYSIOLOGY. 



FLUIDS CONTAINING FORMED ANATOMIC ELEMENTS. 



Seminal fluid, containing sperma- Fluid of the Graafian follicles, 

 tozoids. 



The essential apparatus for secretion is a delicate, homogeneous, 

 structureless membrane, on one side of which, in close contact, is 

 a capillary plexus of blood-vessels, and on the other side a layer 

 of cells the physiologic function of which varies in different situ- 

 ations. 



Secreting organs may be divided into membranes and glands. 



Serous membranes usually exist as closed sacs, the inner surfaces 

 of which are covered by pale, nucleated epithelium, containing a 

 small amount of secretion. 



The serous membranes are the pleura, peritoneum, pericardium, 

 synovial sacs, etc. 



The serous fluids are of a pale amber color, somewhat viscid, 

 alkaline, coagulable by heat, and resemble the serum of the blood ; 

 their amount is but small. The pleural fluid varies from four to 

 seven drams ; the peritoneal from one to four ounces ; the pericardial 

 from one to three drams. 



The synovial fluid is colorless, alkaline, and extremely viscid, 

 from the presence of synovin. 



The function of serous fluids is to moisten the opposing surfaces, 

 so as to prevent friction during the play of the viscera. 



The mucous membranes are soft and velvety in character, and line 

 the cavities and passages leading to the exterior of the body e. g., 

 the gastro -intestinal, pulmonary and genito -urinary. They consist 

 of a primary basement membrane covered with epithelial cells, which 

 in some situations are tessellated, in others, columnar. 



Mucus is a pale, semitransparent, alkaline fluid, containing epi- 

 thelial cells and leukocytes. It is composed, chemically, of water, 

 an albuminous principle (mucin), and mineral salts; the principal 

 varieties are nasal, bronchial, vaginal, and urinary. 



Secreting glands are formed of the same elements as the secreting 

 membranes, but instead of presenting flat surfaces, are involuted, 

 forming tubules, which may be simple follicles e. g., mucous, uterine, 

 or intestinal ; or compound follicles e. g., gastric glands, mammary 

 glands, or racemose glands e. g., salivary glands and pancreas. 

 They are composed of a basement membrane, enveloped by a plexus 

 of blood-vessels, and are lined by epithelial and true secreting cells, 



