238 The Control of Salivary Secretion 



PRIMARY CENTRES OF SALIVARY SECRETION 



The only source of information about the location of the cell 

 bodies of the preganglionic, sympathetic secretory fibres seems to 

 be an investigation by Langley (1892), and it applies exclusively to 

 the submaxillary gland of cats and dogs. Langley stimulated the 

 cervical and thoracic nerves and obtained a secretory response par- 

 ticularly from the second thoracic nerve. This effect was smaller 

 than that evoked by stimulation of the cervical sympathetic trunk ; 

 some flow of saliva usually occurred when the first, third, fourth 

 and fifth thoracic nerves were excited. Vasoconstriction was elicited 

 via the same nerves. No attempts have been made to cause secretion 

 by stimulating the lateral column of the spinal cord in the cor- 

 responding segments. It is not known whether secretion can be 

 evoked reflexly at this level, nor have any supraspinal pathways 

 been explored. The only suggestion of supraspinal fibres acting on 

 the spinal secretory cells can be found in a paper by Grutzner 

 (1873), who stimulated the medulla oblongata electrically and 

 obtained a secretion which ceased when the cervical sympathetic 

 trunk had been cut. 



For the parasympathetic system the nerve cells of the pregan- 

 glionic neurone are situated in the lower brain stem. When study- 

 ing the diabetes produced by puncture of the floor of the fourth 

 ventricle in dogs, Claude Bernard (1856) sometimes observed a 

 flow of saliva; the wound could elicit a secretion both from the 

 parotid and submaxillary glands, but lesions could be made which 

 activated the latter gland only. Similar observations were later made 

 by Eckhard (1869) and Loeb (1870). Loeb associated the secretory 

 effects with damage to the fibres and nuclei of the facial and 

 glossopharyngeal nerves and quoted a case of hypersalivation des- 

 cribed by Meynert in 1863 ; at autopsy an abscess was found in the 

 pons which had perforated into the fourth ventricle and injured 

 the medulla. In his experiments, referred to above, Grutzner (1873) 

 inserted two needles into the medulla and often found this to cause 

 some secretion from the submaxillary gland. When the needles 

 were used as electrodes for electrical stimulation there was an 

 abundant flow of saliva ; after section of the chorda tympani this 

 effect was small, and no secretion at all was obtained when the 

 sympathetic fibres had been cut as well. 



Beck (1898) made a series of transverse sections through the 



