COMPOSITION OF THE SYNOVIAL FLUID MUCUS. 353 



this organic matter has been extracted and mixed with water, it gives to the fluid the 

 peculiar viscidity of the synovial secretion. The reaction of the fluid is faintly alkaline, 

 on account of the presence of a small proportion of carbonate of soda. The fluid, espe- 

 cially when the joints have been much used, usually contains in suspension pale epithe- 

 lial cells and a few leucocytes. The following is the composition of the synovial fluid 

 of the human subject : 



Composition of the Synovial Fluid. (Robin.) 



Water 928'00 



Synovine (called albumen) 64*00 



Principles of organic origin (belonging to the second class of Robin) not estimated. 



Fatty matter 0'60 



Chloride of sodium 



Carbonate of soda 



Phosphate of lime 1*50 



Ammonio-magnesian phosphate traces. 



The observations of Frerichs indicate considerable variations in the composition and 

 general characters of the synovial fluid, dependent upon use of the joints. In a stall- 

 fed ox, the proportion of water to solid matter was 969*90 to 30*10 ; and, in animals 

 that took considerable exercise, the proportions were 948*54 of water to 51*46 of solid 

 matter. In the latter, the fluid was more viscid and contained a larger proportion of 

 synovine with a smaller proportion of salts. It was also more deeply colored and con- 

 tained a larger number of leucocytes. 



Like the serous fluids, the synovial secretion is produced by the general surface of the 

 membrane and not by any special organs. The folds and fringes which have been de- 

 scribed were at one time supposed to be most active in secreting the organic matter, but 

 there is no evidence that they have any such special office. 



The aqueous humor of the eye and the fluid of the labyrinth of the internal ear resem- 

 ble the serous secretions in many regards ; but these fluids, with the vitreous humor, 

 will be considered in connection with the physiological anatomy of the eye and ear. 



Mucus. 



Mucous Membranes. The mucous membranes in different situations present impor- 

 tant peculiarities in structure, many of which have already been considered. "We have 

 described in detail the mucous membrane of the air-passages and of the alimentary canal, 

 in connection with the subjects of respiration and digestion; and the membranes in other 

 parts will necessarily be described in treating of the physiology of the organs in which 

 they are found. It will be sufficient at present to take a general view of the structure 

 of these membranes and the mechanism of the production of the various fluids known 

 under the name of mucus. 



A distinct anatomical division of the mucous membranes may be made into two 

 classes, as follows : First, those provided with pavement-epithelium ; and second, those 

 provided with columnar or conoidal epithelium. All of the mucous membranes line 

 cavities or tubes communicating with the exterior by the different openings in the body. 



The following are the principal situations in which the first variety of mucous mem- 

 branes, covered with pavement-epithelium, are found: The mouth, the lower part of the 

 pharynx, the oesophagus, the conjunctiva, the female urethra, and the vagina. In these 

 situations, the membrane is composed of a chorion made up of inelastic and elastic 

 fibrous tissue, a few fibro-plastic elements, with capillaries, lymphatics, and nerves. The 

 elastic fibres are small and quite abundant. The membrane itself is loosely united to 

 the subjacent parts by areolar tissue. The chorion is provided with vascular papilla?, 

 more or less marked ; but, in all situations, except in the pharynx, the epithelial cover- 

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