MUCOUS SYSTEM. 251 



opening on the free surface. They vary much in size; 

 they are simple or compound. 



Q. What do you understand by the alveolar structure 

 of the mucous tissues? 



t#. They are small superficial cavities found in the gas- 

 tric and intestinal mucous surface by Mr. Hewson, and 

 more accurately described by Mr. Home. They are 

 called alveolar from their resemblance to the cells of bees. 



Q. How do they differ from follicles? 



#. In this, that their mouths are broader than their 

 bottoms. 



Q. State an important fact as to the follicles and 

 alveoli. 



*ft. It has been ascertained that in herbivorous animals, 

 the follicles are more complicated in structure, and secrete 

 a more active juice. In carnivorous animals they are 

 more simple, and resemble alveoli. In omnivorous animals, 

 in man, they are of both kinds on the mucous surface. 



Q. How does follicular secretion differ from glandular, 

 and from exhalation? 



A. In follicles, the secreted fluid is brought directly by 

 the extremities of the arteries; the secreted fluid remains 

 in the follicular cavity to be elaborated before it is thrown 

 out on the organ. 



Q. What is the nature of the membrane lining abscesses 

 and fistuke? 



./?. They are'evidently mucous. 



Q. Under what circumstances do mucous canals close? 



t#. When by any cause an inflammation arises which 

 destroys the mucous surfaces; then the parts in contact 

 cicatrize. 



