Effects of SuprabuJbar Structures 241 



the result of excitation of afferent fibres, particularly taste fibres, 

 acting upon the salivary centres of both sides. The bilateral secre- 

 tory responses usually observed when afferent fibres of one side 

 were stimulated would therefore be due to a partial decussation of 

 the afferent limb of the reflex arc. Claude Bernard (1858) had found 

 that stimulation of the central end of one of the lingual nerves 

 (medial to the submaxillary duct) caused a flow of saliva from both 

 submaxillary glands. Also unilateral section of the lingual nerve 

 causes a supersensitivity to chemical agents in both submaxillary 

 glands (Emmelin, 1956). In his experiments on the human parotid 

 gland Lashley (1916) noticed that a small amount of hydrochloric 

 acid applied to one side of the tongue gave a secretion from both 

 glands but it was particularly marked on the side stimulated. In 

 decerebrate cats Miller (19 13) observed that stimulation of the 

 central end of the lingual nerve brought about an abundant secre- 

 tion from the ipsilateral submaxillary gland, less secretion from the 

 ipsilateral parotid gland and a slight secretion from the contra- 

 lateral submaxillary and parotid glands. When the central end of 

 the glossopharyngeal nerve was stimulated he found a good flow 

 from the ipsilateral parotid gland, less from the ipsilateral sub- 

 maxillary gland and small responses from the contralateral glands. 

 Krasnogorski's (1931) observations on children seem to agree with 

 these findings. When the anterior part of the tongue was stimulated 

 the submaxillary gland was especially affected, whereas stimulation 

 of the lateral and posterior part of the tongue activated predomin- 

 antly the parotid gland. These experiments suggest that the afferent 

 fibres from the mouth act on all the four salivary nuclei of the 

 medulla and particularly the ipsilateral ones, and that the lingual 

 fibres affect more the superior than the inferior nucleus saliva- 

 torius, whereas the opposite is true for the glossopharyngeal fibres. 



EFFECTS OF SUPRABULBAR STRUCTURES 



Secretion of saliva can be evoked reflexly in decorticated dogs 

 and cats (Rothmann, 19 10, 1923 ; Dusser de Barenne, 1920). It can 

 even be elicited in decerebrate animals, for instance by placing some 

 acid on the tongue. The medullary salivary nuclei, therefore, must 

 be able to act as centres for the gustatory reflex. It is obvious, on 

 the other hand, that suprabulbar structures exert excitatory and 

 inhibitory actions on the centres in the brain stem. This is evident 

 from the classical experiments by Pavlov on conditioned salivary 

 p.s.g. — R 



