506 THE SALIVAR Y GLANDS. 



and anaemia of the gland is produced as if the sympathetic alone were 

 being stimulated. Von Frey, using brief stimuli usually lasting about 

 ten seconds observed that the after-action was that of the chorda 

 tympani, and in some cases the increase of blood flow after the stimula- 

 tion appeared to be as great as if the chorda alone had been stimu- 

 lated. 



When, however, the sympathetic is stimulated with weak currents, 

 and the chorda tympani with strong currents, there is, within certain 

 limits, an algebraical summation of effects. And the constriction pro- 

 duced by a weak stimulation of the sympathetic may be more or less 

 annulled by a strong stimulation of the chorda. 



MUTUAL EFFECTS OF THE CRANIAL AND SYMPATHETIC NERVES 

 UPON SECRETION. 



We have already mentioned, under the head of the augmented 

 secretion (p. 496), the effect on the sympathetic saliva of a previous 

 brief stimulation of the cerebral nerve. 



When the chorda tympani and the sympathetic nerve in the cat 

 are stimulated simultaneously with minimal currents of not too long 

 duration, the amount of saliva obtained is greater than that which is 

 obtained from either nerve alone. 1 In the dog the same effect may also 

 be seen ; at any rate, if the gland is in a state to allow the sympathetic 

 to produce an augmented secretion. 



As the currents are increased in strength, the amount of the saliva 

 obtained by simultaneous stimulation becomes rapidly less and less in 

 excess of that obtained by stimulating the chorda alone. And with a 

 very moderate strength of sympathetic stimulation, the amount of saliva 

 obtained by simultaneous stimulation falls below, and it may be very 

 considerably below, that which is afforded by stimulation of the chorda 

 by itself. The secretion is rapid for five or ten seconds, and then 

 speedily becomes slow. The retarding effect of the sympathetic we may 

 reasonably attribute to the diminution in the blood supply to the 

 gland which it brings about. 



In the parotid gland of the cat similar effects are seen on excitation 

 of the sympathetic and of Jacobson's nerve. The sympathetic nerve in 

 the dog has a very marked retarding action upon the flow of saliva pro- 

 duced by Jacobson's nerve from the parotid gland, and it may stop the 

 flow altogether (cf. also p. 498). 



Prolonged stimulation of the sympathetic reduces the irritability of 

 the gland, so that, on subsequent stimulation of the chorda tympani, the 

 saliva only appears after a long latent period, and but gradually acquires 

 its normal rate of flow. 



Czermak 2 was the first to call attention to the retarding action of the 

 sympathetic upon the chorda secretion. He stated that in the dog, the 

 sympathetic stopped the chorda secretion, and produced a condition of the 

 gland of such nature that it did not for some time respond to stimulation of 

 the chorda tympani. He referred the action to inhibitory fibres, which he 

 believed to be present in the sympathetic. Eckhard 3 considered that the 



1 Langley, Journ. PhyxioL, Cambridge and London, 1878, vol. i. p. 102. 



2 Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1857, Bd. xxv. S. 3. 



3 Beitr. z. Anat. u. Pliysiol. (Eckhard}, Giessen, 1860, Bd. ii. S. 95. 



