CHAPTER XII 

 THE CONTROL OF SALIVARY SECRETION 



Our knowledge of the control of salivary secretion originates from 

 different sources. The first indication of the existence of a "salivary 

 centre" was obtained by chance in experiments in which irritative 

 damage was done to various parts of the brain stem. Transverse 

 sections through the central nervous system later on served to 

 locate the region from which a salivary reflex can be evoked. After 

 degenerative section of the preganglionic secretory nerves the posi- 

 tion of their cell bodies in the central nervous system could be 

 found by microscopic examination. Some knowledge of the control 

 of salivary secretion has been gained by clinical observations and 

 in experiments in which drugs have been applied to different parts 

 of the central nervous system. The most precise information has 

 been obtained by electrical stimulation of restricted areas, followed 

 by histological control. 



The double supply of secretory fibres to the glands from the two 

 divisions of the autonomic nervous system makes it necessary to 

 decide, in stimulation experiments, whether parasympathetic or 

 sympathetic fibres were activated. This can be done by cutting the 

 fibres or by using specific inhibitors, such as atropine and ergot- 

 amine. In several of the investigations reported in the literature 

 such precautions were omitted and we do not know which type of 

 fibres were excited. When pronounced and well-maintained secre- 

 tory responses were obtained it can usually be concluded that the 

 parasympathetic mechanism was at work. It should further be kept 

 in mind that stimulation of various parts of the central nervous 

 system may increase the discharge of adrenaline from the supra- 

 renal medulla, thereby causing a flow of saliva ; in experiments on 

 glands relatively sensitive to adrenaline such as the submaxillary 

 or sublingual gland of the cat, or the parotid gland of the rabbit, 

 it seems advisable to remove or denervate the adrenals. For 

 example stimulation of the central end of the sciatic nerve causes 

 a flow of saliva which, at least in part, is due to adrenaline, released 

 reflexly from the adrenal medulla. 



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