5 1 2 THE SALIVAR Y GLANDS. 



It may, however, be doubted whether there is such a difference in the 

 maximum pressure. In the observations I have made on the point, 

 stimulating alternately the chorda tympani and the sympathetic, the 

 sympathetic has given a perceptible though slight and brief rise of 

 pressure at approximately the maximum pressure obtainable from the 

 chorda tympani. 



EEFLEX INHIBITION OF THE SALIVARY SECRETION. 



During the progress of secretion, a certain decrease in the rate of 

 flow, or even a cessation, may be caused by stimulation of afferent 

 nerves. Such an effect might be due to select the most probable 

 causes either to an inhibition of the central secretory centre, or to a 

 constriction of the blood vessels of the gland. The experiments have 

 not, however, been directed to an accurate determination of the method 

 of production of reflex inhibition. . 



Pawlow l states that the slow secretion induced by partial dyspnoea, 

 or by curari, is decreased or temporarily stopped by stimulation of the 

 sciatic for one or two minutes with a particular strength of current, or 

 by exposure of the abdominal viscera. The experiments given can 

 hardly be considered to be conclusive, and Buff 2 finds that, quite apart 

 from stimulation, the secretion occurring in the conditions of Pawlow's 

 experiments is not itself constant in rate. 



ACTION OF ALKALOIDS UPON THE SALIVARY GLANDS. 



There are obviously a number of ways in which a substance intro- 

 duced into the blood might cause a secretion of saliva. It might 

 stimulate the peripheral endings of sensory nerves and produce a reflex 

 secretion ; it might stimulate some part of the central nervous system, 

 the connections of the visceral nerve-fibres with the local nerve-cells, 

 the nerve-cells directly, the nerve-endings in the gland, or finally the 

 gland-cells directly. Of several of these modes of action we have no 

 certain example. We shall confine our attention to those alkaloids, 

 the effects of which have most served as a basis of physiological 

 deduction. 3 



Atropine. Atropine arrests the normal secretion from the glands 

 of the mouth, nose, and pharnyx, so that the whole mucous membrane 

 becomes dry. The arrest is due -to a paralysis of the cranial secretory 

 nerves, the strongest stimulation of them no longer causing a secretion. 4 

 In the dog, 10 to 15 mgrms. of atropine, when injected into a vein, pro- 

 duce the paralysis; in the cat, 3 to 5 mgrms. are sufficient. Considerably 

 smaller doses than these reduce to very small limits the secretory power 

 of the nerves ; hence, in determining the minimal amount of atropine 

 required to produce paralysis, it is advisable to stimulate the nerve for 

 a minute or more, and to repeat this after a few minutes' interval. 



The sympathetic nerve is either not paralysed at all, or only by a 



1 Arch. f. d. ges. PhysioL, Bonn, 1878, Bd. xvi. S. 272 (experiments made on the sub- 

 maxillary gland of the dog). 



2 Beitr. z. Anat. u. Physiol. (EcMard), Giessen, 1888, Bd. xii. S. 3. 



3 A few only of the original papers dealing with this subject can be given here ; fuller 

 references will be found in treatises on pharmacology. 



4 Keuchel, "Das Atropin mid die Hemmungsnerven," Dorpat, 1868; Heidenhain, 

 Arch.f. d. ges. Physiol., Bonn, 1872, Bd. v. S. 309. 



