PHYSI0L001 OP Till. DIGESTIVE QLA1 123 



the process by which this glandular activity is controlled. Two mechan- 

 isms of control arc known: I by the nervous Bystem, and (2) by means 

 of hormones. 



Nervous Control. Control through the tier a system is mosl marked 



— indeed if may be the only means of control in glands which hav< 

 produce their secretion promptly, whereas hormone control pre- 

 dominates in those in which prompl changes in tory activity are not 

 required. Thus, nervous control alone is present in the salivary glands, 

 whereas hormone control is predominanl in the pancreas, intestinal 

 glands and liver. The gastric glands are partly under nervou trol, 



and partly under hormone control. It should be pointed out here that 



the glands of the body other than the digestive glands are also Bubjecl to 

 nervous or hormone control according to the promptness with which they 

 arc required to secrete. The lachrymal and sweat glands, and the venom 

 glands of reptiles, for example, are practically entirely under nerv< 

 control, whereas most of the ductless glands, with the exception of the 

 adrenals, are mainly under the influence of hormoi 



The exact nature of the nervous control of glandular function fa 

 therefore, been mosl extensively studied iii the salivary glands, and that 

 of the hormonic in the pancreas. With regard to the salivary glands, 

 the following points are of importance: Their nerve supply comes from 

 two sources: the cerebral autonomic, and the sympathetic autonomic 

 see page s 77 . These two nerve supplies have usually an opposite intlu 

 ence on the secretory activity of the glands, and very frequently also on 

 the vascular changes that accompany secretory activity. 



On account of its ready accessibility, the submaxillary gland in the 

 dog and cat has been most thoroughly investigated. Th< bral auto- 



nomic nerve in this case is represented by the chorda tympani, and the 



sympathetic autonomic by postganglionic fibers that run from the 



superior cervical ganglion to the gland along its hi 1 vessels Fig, 1 : 



After tying a cannula into the duct of the gland, it will be found in 

 dog that stimulation of the chorda tympani produces an immedial 

 abundant secretion of thin watery saliva a mpanied by a mar' 



dilatation of the hi I \essels of the gland. 



That this Becretion is not dependent on the vasodilatation is easily 

 shown by repeating the experiment after administering a sufficient d 

 id' atropine to paralyze the secreting cells, stimulation of the nerve then 

 produces a vasodilatation bul no secretion. The sane elusion 



arrived at by an experiment of an entirely different nature: namely, by 



observing the pressure produced in the duct when the chorda tympani is 

 stimulated. This pressure rises considerably above that in the art 

 so that no Buch physical process as mere diffusion can be held accountal 



