MUCUS. 327 



The principal secretions met with in the animal body are as 

 follows : 



1. Mucus. 6. Saliva. 



2. Sebaceous matter. 7. Gastric juice. 



3. Perspiration. 8. Pancreatic juice. 



4. The tears. 9. Intestinal juice. 



5. The milk. 10. Bile. 



The last five of these fluids have already been described in the 

 preceding chapters. We shall therefore only require to examine 

 at present the five following, viz., mucus, sebaceous matter, per- 

 spiration, the tears, and the milk, together with some peculiarities 

 in the secretion of the bile. 



1. Mucus. Nearly all the mucous membranes are provided with 

 follicles or glandulae, in which the mucus is prepared. These folli- 

 cles are most abundant in the lining membrane of the mouth, nares, 

 pharynx, oesophagus, trachea and bronchi, vagina, and male urethra. 

 They are generally of a compound form, consisting of a number of 

 secreting sacs or cavities, terminating at one end in a blind ex- 

 tremity, and opening by the other into a common duct by which 

 the secreted fluid is discharged. Each ultimate secreting sac or 

 follicle is lined with glandular epithelium (Fig. 102), and surround- 

 ed on its external surface by a network of capillary bloodvessels. 

 These vessels, penetrating deeply into the F . 1Q2 



interstices between the follicles, bring the 

 blood nearly into contact with the epithelial 

 cells lining its cavity. It is these cells 

 which prepare the secretion, and discharge 

 it afterward into the commencement of the 



excretory duct. "FOLLICLES OF A COM- 



The mucus, produced in the manner POUND MCCOUS GLANDULE. 



, , ., , . , ,, n t From the human subject. (After 



above described, is a clear, colorless fluid, K o inker.)-*. Membrane of the 

 which is poured out in larger or smaller foiiscie. j, c. Epithelium of the 



t n fl i same. 



quantity on the surface ot the mucous 



membranes. It is distinguished from other secretions by its vis- 

 cidity, which is its most marked physical property, and which 

 depends on the presence of a peculiar animal matter, known under 

 the name of mucosine. When unmixed with other animal fluids, 

 this viscidity is so great that the mucus has nearly a semi-solid or 

 gelatinous consistency. Thus, the mucus of the mouth, when ob- 

 tained unmixed with the secretions of the salivary glands, is so 



ff 



