THE FUNCTIONS OF THE DIGESTIVE ORGANS. 485 



Such a point of view is particularly advantageous now that we come to 

 consider the functions of the various organs in the digestive canal. They 

 are of most diverse nature according to the part of the digestive stratum 

 in which they are found. Let us begin with the functions of the upper end 

 of the alimentary canal, the mouth. In it the food which has been pre- 

 pared in various ways, is chewed up into small pieces and intimately mixed 

 with the saliva. In this way the morsels are prepared for digestion. The 

 saliva comes from the salivary glands and from the mucous membrane of 

 the mouth. There are three pairs of the former, which may be dis- 

 tinguished chiefly by the nature of the fluids they secrete. The parotid 

 (near the ear) gland produces a thin watery fluid containing chiefly albumin 

 and salts. It is spoken of in general as an albuminous gland. Small glands 

 of this nature are found as well in the mucous membrane of the nose and 

 mouth. The other glands are the so-called mucous glands. They, in con- 

 trast to the former, furnish a glairy, or more ropy secretion, due to the 

 mucin which it contains. To this class of glands belong, in the case of most 

 animals, the submaxillary and sublingual glands. Small mucous glands 

 are found distributed in the mouth, throat, and oesophagus. This distinc- 

 tion between two kinds of glands is not a sharp one. Thus the lower jaw 

 of man contains glands which yield a thin secretion rich in albumin as well 

 as one of a more mucous nature. 



The secretion from each separate gland may be examined by construct- 

 ing fistulas in the exit ducts, or more simply by introducing a canula into 

 the mouth of the duct from where it discharges outward. Normally a 

 mixture of the secretions from all of the glands comes into action. The 

 extent to which the different glands take part in the formation of the 

 saliva varies. The secretion of the glands is dependent upon quite a 

 number of outside influences, as J. P. Pawlow 1 has quite recently called 

 to our attention. In the exercise of their function, they are dependent 

 upon nervous influences. The innervation of each gland is twofold. 

 Cerebral and sympathetic fibers lead to each. The submaxillary gland 

 contains fibers from the chorda tympani, and, on the other hand, fibers 

 enter the blood-vessels of the gland from the sympathetic system. This 

 double innervation also corresponds to the nature of the secretion. 

 By stimulating the cerebral fibres, in other words, those of the chorda 

 tympani, an abundant secretion of a thin liquid is produced; whereas, by 

 stimulating the sympathetic nerve, only a few drops of a viscid liquid rich 

 in mucin are obtained. The sublingual gland behaves quite similarly. The 

 parotid gland is also partly dependent upon the cerebral nervous system 

 (in this case the glossopharyngeal nerve) and partly on the sympathetic. 



For some time it was belie.ved that the influence of the nerves which 

 reach these glands could be explained by an action upon the blood-vessels. 



1 Ergeb. Physiol. (Asher and Spiro) Jahrg. III., Abt. I, p. 177 (1904). 



