DIGESTION 369 



Paralytic Secretion. When the chorda tympani is divided, a slow 

 ' paralytic ' secretion from the submaxillary gland begins in a few 

 hours, and continues for a long time accompanied by atrophy of 

 the gland. There is also a secretion of the same kind from the 

 submaxillary on the opposite side, but it is less copious. This is 

 called the ' antilytic ' secretion, which is most pronounced in the first 

 few days after the operation, and seems to be a transient pheno- 

 menon. It can be at once abolished by section both of the chorda 

 and the sympathetic on the corresponding side, and is therefore due 

 to impulses arising in the central nervous system. The cause of the 

 paralytic secretion has not been fully made out. If within two or 

 three days of division of the chorda the sympathetic on the same 

 side is cut, the secretion is greatly diminished or stops altogether ; 

 and it is concluded that up to this time it is maintained by impulses 

 passing along the sympathetic to the gland from the salivary centre, 

 the excitability of which has been in some way increased by division 

 of the chorda, possibly by some such degenerative process in the 

 cells as the changes seen in cerebro-spinal motor cells whose 

 axons have been divided (p. 756). This may also account for the 

 antilytic secretion. But if section of the sympathetic is not per- 

 formed for several days, it has no effect on the paralytic secretion, 

 which at this stage seems to depend on local changes in or near the 

 gland itself, leading to a mild continuous excitation of those nerve- 

 cells on the course of the fibres of the chorda to which reference has 

 already been made. Section of the sympathetic alone causes neither 

 secretion nor atrophy, nor does removal of the superior cervical 

 ganglion. The histological characters of the gland-cells during 

 paralytic secretion are those of ' rest.' 



Reflex Secretion of Saliva. The reflex mechanism of salivary 

 secretion is very mobile, and easily set in action by physical and 

 mental influences. It is excited normally by impulses which 

 arise in the mouth, especially by the contact of food with the 

 buccal mucous membrane and the gustatory nerve-endings. 

 The mere mechanical movement of the jaws, even when there is 

 nothing between the teeth, or only a bit of a non-sapid sub- 

 stance like indiarubber, causes some secretion. The vapour of 

 ether gives rise to a rush of saliva, as does gargling the mouth 

 with distilled water. The smell, sight, or thought of food, and 

 even the thought of saliva itself, may act on the salivary centre 

 through its connections with the cerebrum, and make ' the teeth 

 water.' A copious flow of saliva, reflexly excited through the 

 gastric branches of the vagus, is a common precursor of vomit- 

 ing. The introduction of food into the stomach also excites 

 salivary secretion. 



The researches of Pawlow and his pupils have shown that the 

 salivary glands are not excited indifferently by everything which 

 comes into contact with the buccal mucous membrane. A 

 remarkable adaptation exists between the properties of food or 

 foreign bodies introduced into the mouth and their effects upon 

 the secretion of saliva. When solid dry food is given to a dog 

 saliva is copiously poured out ; much less is secreted when the 



24 



