MUCUS. 197 



shown that the latter are not to be distinguished, in their natural 

 state, from the normal cytoid corpuscles in mucus (p. 146). Vibri- 

 ones and microscopic fungoid growths must be considered as of 

 incidental occurrence. 



It should also be added that a fluid possessing all the characters 

 ascribed to mucus is sometimes secreted in certain cysts. 



The quantity secreted by the mucous membranes cannot be ascer- 

 tained with accuracy. Valentin believed the amount to be exceed- 

 ingly small, or even absolutely nothing, in the normal state. Cer- 

 tainly it is only in irritative congestion, or inflammation, that the 

 amount becomes considerable ; but then there is a transudation or 

 exudation, or both, mixed with the true mucus. 



Origin. It has been stated that true mucus (i. e. the fluid portion) 

 is secreted by the epithelial cells of the follicles or of the general 

 surface of mucous membranes, except when they line the ducts of 

 glands; while the epithelial cells of the latter secrete saliva, urine, 

 &c., according to the gland in which they exist. It is, therefore, the 

 epithelial cells on a mucous membrane, and not the mucous mem- 

 brane merely as such, which manifest specific vital properties and 

 specific secretory functions (p. 195). 



It has been suggested that the true mucus is derived from a sort 

 of decomposition or partial disintegration of the epithelial cells. 

 Though this chemical view may be correct so far as it implies that 

 mucus as found is different from the same while still inclosed within 

 the epithelial cells, there are sufficient physiological grounds for the 

 belief that mucus is, at any rate, originally elaborated within the 

 epithelial cells, from the plasma of the blood. It might be antici- 

 pated that the form of the epithelium, whether scaly or conoidal, 

 would correspond with a difference in the fluid secreted. 



The cytoid (mucus) corpuscles are, by some, said not to be present 

 in normal mucus. Kolliker maintains that they "are abnormal, 

 but almost constantly present," in the mucus of the oral cavity; 

 being a "kind of exudation or pus-corpuscle, with which they have 

 the closest possible resemblance in structure" (p. 466). Lehmann 

 seems rather to indorse the idea that the mucus-corpuscles, so called, 

 are merely abortive epithelial cells. 



While we agree with Kolliker that the cytoid corpuscles consti- 

 tute no part of the true mucus, we cannot regard them as abnormal 

 products ; nor admit, on the other hand, that they have any deve- 

 lopmental relation to the epithelial cells. We believe them to be 



