758 PHYSIOLOGY OF DIGESTION AND SECRETION. 



are really intercalated in the course of the fibers to the sublingual 

 gland, while the nerve cells with which the submaxillary fibers make 

 connection are found chiefly in the hilus of the gland itself. 



Paralytic Secretion. — ^A remarkable phenomenon in connection 

 with the salivary glands is the so-called paralytic secretion. It has 

 been loiown for a long time that if the chorda tympani is cut the 

 submaxillary gland after a certain time, one to three days, begins to 

 secrete slowly, and the secretion continues uninterruptedly for a long 

 period — as long, perhaps, as several weeks — and eventually the gland 

 itself undergoes atrophy. Langley states that section of the chorda 

 on one side is followed by a continuous secretion from the glands 

 on both sides; the secretion from the gland of the opposite side he 

 designates as the antiparalytic or antilytic secretion. After section 

 of the chorda the nerve fibers peripheral to the section degenerate, 

 the process being completed within a few days. These fibers, how- 

 ever, do not run directly to the gland cell; they terminate in 

 synapses around sympathetic nerve cells placed somewhere along 

 their course, — in the sublingual ganglion, for instance, or within the 

 gland substance itself. It is the axons from these second nerve units 

 that end around the secreting cells. Langley has accumulated some 

 facts to show that within the period of continuance of the paralytic 

 secretion (five to six weeks) the fibers of the sympathetic cells are 

 still irritable to stimulation. He is inclined to believe, therefore, that 

 the continuous secretion is due to a continuous excitation, from some 

 cause, of the local nervous mechanism in the gland. A natural 

 extension of this view which has been suggested (Pawlow) is 

 that normally the activity of the sympathetic cells or of the 

 secreting cells is kept in check by inhibitory fibers. After section 

 of the chorda the action of these fibers falls out and the secre- 

 tion continues until the glandular tissue undergoes atrophy. 



Normal Mechanism of Salivary Secretion. — Under normal con- 

 ditions the flow of saliva from the salivary glands is the result of 

 a reflex stimulation of the secretory nerves. The sensory fibers 

 concerned in this reflex must be chiefly fibers of the glossopharyn- 

 geal and lingual nerves supplying the mouth and tongue. Sapid 

 bodies and various other chemical or mechanical stimuli applied 

 to the tongue or mucous membrane of the mouth produce a 

 flow of saliva. The normal flow during mastication must 

 be effected by a reflex of this kind, the sensory im- 

 pulse being carried to a center and thence transmitted through 

 the efferent nerves to the glands. It is found that section 

 of the chorda prevents the reflex, in spite of the fact that the 

 sympathetic fibers are still intact. No satisfactory explanation 

 of the normal functions of the secretory fibers in the sympathetic 

 has yet been given. Various authors have suggested that possibly 



