42 Innervation of the Glandular Elements 



increases the resting membrane potential; this occurs both in his 

 "type i" and "type 2" responses, which he assumes to originate 

 from alveolar and demilune cells, respectively. According to Gayda 

 (1925) it is even possible to demonstrate a secretory response to a 

 single shock applied to the chorda ; other investigators have found 

 this to be the case in some experiments only (Beznak and Farkas, 



!93 6 -37)- 



On repetitive stimulation the rate of salivary flow increases with 

 the increasing rate of stimulation, as analysed by Beznak and 

 Farkas (1936-37). When trying to estimate the frequency needed 

 to obtain a maximal response different results have been obtained, 

 for instance 40 (Wedensky, 1892), 10-30 (Kupalov and Skipin, 

 1934), 36 (Rosenblueth, 1932), 30-40 (Bruner and Kozak, 1957), 

 3 (Beznak and Farkas, 1936-37), 9 (Wills, 1941), 10 per second 

 (Diamant, Enfors and Holmstedt, 1959). At least in the submaxil- 

 lary gland of the cat 10-20 stimuli per second give a maximal 

 secretory response. With this frequency, the high rate of flow can 

 be almost maintained, for hours ("die Geduld des Beobachters 

 erschopft sich fruher als die Erregbarkeit des Nerven und der 

 Druse", according to Heidenhain), the gland delivering an amount 

 of saliva as big as its own weight in a few minutes. 



Lundberg's experiments indicate that the parasympathetic fibres 

 excite both the alveolar and the demilune cells. It is, in fact, not 

 possible to obtain a higher rate of salivary flow with any chemical 

 or nervous stimuli than that elicited by stimulation of the chorda 

 (Emmelin, 1955a). It seems reasonable to assume that the chorda 

 fibres are able to excite all the secretory elements of the sub- 

 maxillary gland to maximal activity. After destruction of some of 

 the parasympathetic fibres, stimulation of the remaining ones 

 causes cytological signs of secretory activity in some acini, whereas 

 other neighbouring acini seem to be at rest (Mansfeld, Hecht and 

 Kovacs, 1931; Hillarp, 1949). There is thus no spread of stimu- 

 lation from some nerve fibres to all the glandular elements. The 

 results have been taken as evidence to show that diffusion of the 

 chemical mediator from its site of liberation in contact with one 

 cell to adjacent cells does not play a major role (Hillarp, 1949). 

 Under certain experimental conditions such a spread may of 

 course take place; after the administration of a cholinesterase 

 inhibitor, for instance, stimulation of the chorda may even evoke 

 a secretion in the contralateral submaxillary gland and a fall in the 



