48 Innervation of the Glandular Elements 



of the gland when it has acted on the gland cells. In addition, 

 cholinesterase has been found in saliva (McCance, Brown, Comline 

 and Titchen, 1951). For the understanding of the mode of action 

 of acetylcholine on the gland cell it would be interesting to know 

 whether the transmitter can reach the inner membrane of the 

 secretory cell, and whether it has any action on it. However, neither 

 the fact that acetylcholine causes a secretion when injected through 

 the duct (Emmelin, Muren and Stromblad, 1954), nor the finding 

 that acetylcholine might possibly appear in saliva on stimulation 

 of the chorda in the presence of eserine (Feldberg and Guimarais, 

 1935) seems to throw any light on that problem. 



In man stimulation of the chorda tympani has been found to 

 produce a flow of saliva from the submaxillary gland (Diamant, 

 Enfors and Homstedt, 1959). 



The sympathetic secretory and motor innervation. The salivary 

 response to sympathetic stimulation is much more variable and 

 usually much smaller than that obtained on stimulation of the 

 parasympathetic. Marked differences in the effect are found be- 

 tween different species and also between the various glands of the 

 same species. General conclusions as regards the existence and 

 distribution of sympathetic secretory and motor fibres should 

 therefore be made with some caution. In the cat, for instance, 

 sympathetic stimulation usually causes a lively flow of saliva from 

 the submaxillary gland, but only a scanty flow from the parotid 

 gland; in some cats, however, the response of the submaxillary 

 gland is very small, or in exceptional cases, completely lacking. In 

 the dog, saliva is obtained from the submaxillary gland, but scarcely 

 any from the parotid gland. In rabbits, the response of the parotid 

 is more marked than that of the submaxillary gland (Nordenfelt 

 and Ohlin, 1957). 



A common finding is that the flow of saliva, whether rapid or 

 slow, is short-lasting; it diminishes quickly and often ceases wholly 

 in spite of continued stimulation of the sympathetic fibres. This is 

 very likely one of the observations that has led to the conception 

 that the effect of the stimulation is to expel saliva already present 

 in the ducts of the gland. Mathews (1898), for instance, suggested 

 that the flow of saliva from the submaxillary glands of cats and 

 dogs evoked by stimulation of the cervical sympathetic trunk is 

 due solely to the activation of a contractile mechanism. For an 

 effect to be obtained, the ducts should consequently have to con- 



