40 Innervation of the Glandular Elements 



trunk. The flow of saliva observed on stimulation of the trunk may 

 be due to excitation of motor fibres innervating contractile elements 

 in the gland which expel saliva already present in the ducts 

 (Mathews, 1898). Alternatively, a flow of saliva seen during stimu- 

 lation of the sympathetic nerve may be caused by sympathin 

 diffusing from the vasoconstrictor nerve terminals to the secretory 

 cells (Richins and Kuntz, 1953). 



The enumeration of the different types of fibres which may 

 supply the salivary glands is not limited to those so far described. 

 Several investigators have suggested that the parasympathetic 

 nerve contains vasoconstrictor fibres (e.g. Frohlich and Loewi, 

 1906). The fact that a flow of saliva induced by parasympathetic 

 stimulation may be diminished by sympathetic stimulation has led 

 to the suggestion that the sympathetic trunk carries inhibitory 

 secretory fibres for the gland (Czermak, 1857). Claude Bernard 

 (1862) and Bradford (1888), in attempts to explain the ''paralytic 

 secretion" seen after section of the chorda-lingual nerve, postulated 

 the presence of such inhibitory fibres in the parasympathetic nerve. 

 Histological investigations led Kuntz and Richins (1946) to the 

 conclusion that the parasympathetic, and not the sympathetic, 

 nerve contains motor fibres for the contractile elements of the 

 salivary glands, the myoepithelial cells. Finally, it should be re- 

 called that it was as a result of investigations on the salivary glands 

 that Heidenhain (1878) advanced the hypothesis of trophic and 

 secretory fibres, further elaborated by Babkin and extensively 

 discussed in his monograph (1950). 



An investigation by Graham and Stavraky (1953) is of particular 

 interest. The experiments of these authors indicate that whereas 

 low concentrations of acetylcholine have the well-known secretory 

 and vasodilator effects, higher concentrations tend to cause vaso- 

 constriction and reduce the flow of saliva. Acetylcholine was sup- 

 plied either by intra-arterial injections of small and big doses of the 

 drug or by stimulation of the chorda tympani ; in some experiments 

 eserine was given. The usual vasodilatation caused by stimulation 

 of the chorda tympani could for instance be replaced by constric- 

 tion if big doses of eserine or acetylcholine were given, and with 

 this the flow of saliva diminished. 



To sum up : 



1. From the experiments of Graham and Stavraky it can be 

 inferred that nerve fibres, which ordinarily cause vasodilation or 



