242 The Control of Salivary Secretion 



secretion, extensively dealt with in his monograph Conditioned 

 reflexes (1940) and from all the observations which resulted from 

 Pavlov's pioneer work (see for instance Lashley, 1916; Kras- 

 nogorski, 1931 ; Wolff, 1937). Numerous other examples of physio- 

 logical or clinical observations indicative of an influence on the 

 medullary secretory centres from higher levels could be quoted. 

 Experiments in which salivary secretion could be elicited by elec- 

 trical stimuli or certain drugs applied locally to various suprabulbar 

 structures will be described later on. Inhibition of salivary secretion 

 can, in most instances, be explained only as due to an inhibitory 

 influence of higher regions on the medullary centres ; there is no 

 reason to believe in the existence of peripheral inhibitory fibres to 

 the glands, and a diminished secretion caused by hyperactivity in 

 the sympathetic vasoconstrictor fibres, as described in Chapter VII, 

 is certainly in most cases only of secondary importance. Inhibition 

 of secretion is seen in sleep (see for instance Schneyer, Pigman, 

 Hanahan and Gilmore, 1956). Similarly, the reflex response to 

 lemon juice was found to be reduced by hypnosis (Jenness and 

 Hackman, 1938). The dryness of the mouth in fear is well known. 

 Knowledge of this emotional effect was made use of long ago in the 

 Indian rice test; a suspect unable to swallow his rice because of 

 lack of saliva was assumed to be afraid of detection, i.e. to be guilty. 

 According to Lourie (1943) the flow of parotid saliva is extremely 

 abundant in infancy and declines rapidly to the age of 5 years, then 

 falling off more gradually until early puberty. Lourie assumes that 

 during these first years higher centres mature and gradually gain 

 an inhibitory control over the medullary salivary centres. It may be 

 pointed out that Krasnogorski (1931) obtained greater secretory 

 response in older than in younger children. This discrepancy might 

 be due to the fact that the latter investigator studied secretion 

 elicited reflexly by citric acid, whereas Lourie collected saliva 

 without application of any stimuli except those always present in 

 such experiments. 



Clinical experience provides many further samples of disturb- 

 ance in the secretion of saliva in diseases of the central nervous 

 system, for instance the hypersalivation in parkinsonism. In many 

 cases of epilepsy, hypersalivation has been mentioned as a symp- 

 tom (see Penfield and Jasper, 1954, and for animal experiments 

 Hunter and Jasper, 1949). In the first case of "diencephalic auto- 

 nomic epilepsy", described by Penfield (1929), a cholesteatoma in 



