MUCUS. 357 



ing from the air-cells and the bronchial tubes less than -^ of an inch in diameter, which 

 are not provided with mucous glands. This variety of mucus is alkaline and is quite 

 similar to nasal mucus in its appearance and general characters. 



Mucus secreted by the Mucous Membrane of the Alimentary Canal. Throughout the 

 alimentary canal, from the mouth to the anus, the lining membrane secretes a certain 

 quantity of mucus, which does not differ very much from the mucus found in other situa- 

 tions. This secretion appears to take place independently of the act of digestion, and 

 the mucus in most parts of the tract is not known to possess any peculiar digestive prop- 

 erties. By ligating all of the salivary ducts, the buccal mucus has been procured. This 

 secretion is produced by the cells covering the general surface of the membrane and is 

 mixed with the secretion of the isolated follicular and racemose glands of the mouth. 

 An analogous secretion is produced by the mucous membrane of the pharynx and oesoph- 

 agus. During the intervals of digestion, a viscid, alkaline secretion covers the mucous 

 membrane of the stomach. The digestive secretions of the small intestine are so viscid 

 that it has been found impossible to separate them from the true mucous secretion ; but 

 undoubtedly a secretion of ordinary mucus is constantly taking place from the lining 

 membrane of both the small and the large intestine. This secretion probably has a 

 purely mechanical function, serving to lubricate the membranes and facilitate the move- 

 ments of the opposing surfaces against each other. 



The mucous membrane of the gall-bladder produces quite an abundant secretion ; but 

 this is always mixed with the bile, and it will be considered in connection with the com- 

 position of this fluid, although it is not known to possess any peculiar properties. 



Mucus of the Urinary Passages. A small quantity of mucus is secreted by the uri- 

 nary passages. This is present in the normal urine, in the form of a very slight, cloudy 

 deposit, which forms after the urine has been allowed to stand for a few hours. A cer- 

 tain amount of secretion takes place from the mucous membrane of the bladder, which, 

 as we have seen, does not possess glands except near the neck. This secretion is 

 produced in very small quantity, and it may be recognized in the urine by the ordinary 

 microscopical characters of mucus. 



Mucus of the Generative Passages. The vagina secretes a small quantity of mucus, 

 which differs from the secretions of the other mucous membranes in being distinctly acid 

 and almost entirely wanting in viscidity. The mucus of the neck of the uterus is clear, 

 viscid, and distinctly alkaline. This is ordinarily produced in small quantity, but it is very 

 abundant during pregnancy. It is the result of the action chiefly of the large, rounded 

 glands found in this situation. The mucus of the body of the uterus and of the Fallopian 

 tubes is alkaline, of a grayish color, and slightly viscid. The secretions of these parts 

 are greatly modified during menstruation. These considerations, however, belong prop- 

 erly to the subject of generation and will be taken up more fully hereafter. 



Oonjunctival Mucus. A small quantity of a viscid secretion constantly covers the 

 conjunctival mucous membrane, and this is a mixture of the secretion of the membrane 

 itself with the fluid produced by the little mucous glands found near the internal angle of 

 the eye. A peculiarity of this variety of mucus is that it becomes white, like coagulated 

 albumen, by the action of pure water. A peculiarity of the mucus from the conjunctiva, 

 the urethra of the male, and the vagina, is that they readily become virulent when 

 secreted in abnormal quantity. They then contain a large number of leucocytes and have 

 a more or less puriform character. 



General Function of Mucus. The smooth, viscid, and adhesive character of mucus, 

 forming, as this fluid does, a coating for the mucous membranes, serves to protect these 

 parts, enables their surfaces to move freely one upon the other, and modifies to a certain 

 extent the process of absorption. This function is entirely independent of the function 

 of some of the mucous glands, as the follicles of Lieberkuhn, which produce secretions 

 only at particular times. 



