EFFECT OF VARIATIONS IN THE BLOOD SUPPLY. 509 



At a certain further stage of compression of the carotid, stimulation 

 of the chorda will still cause an increase of blood flow from the gland, 

 but the blood issuing from it, instead of being of an arterial colour, will 

 be of a venous colour. In this case Heidenhain finds that the amount 

 of saliva obtained by a given stimulus will be less than normal. 



When the artery is so far compressed that little blood flows through 

 the gland, and the chorda causes no increase in it, there is naturally a 

 great decrease in the amount of saliva obtained by a given stimulus. 

 If the stimulus last about a minute only, the decrease is in fact nearly 

 as great as if the blood supply be entirely cut off. On allowing the 

 blood to flow again through the gland, the chorda saliva does not at 

 once attain its normal amount. Brief closure of the artery causes more 

 or less protracted diminution in the efficiency of the chorda; it may be 

 noted that the vaso-dilator effect of the chorda recovers more quickly 

 than its secretory effect. 



The following example, taken from Heidenhain, 1 may be given to illustrate 

 some of the points mentioned above : Dog, arteries to head tied, except left 

 carotid. Wharton's duct connected with a tube graduated in millimetres. 

 Gland-vein opened. The chorda tympani was stimulated for one minute, and 

 the rise in millimetres of the saliva in the tube was noted each five seconds. 



Saliva flow. -0, 20, 70, 50, 55, 45, 36, 30, 27, 29, 30, 28 = 410. 



The artery was then clamped for five minutes ; during the last minute the 

 chorda was stimulated, the blood flow from the vein was very slight. 



Saliva flow. 0, 0, 21, 32, 33, 17, 14, 8, 6, 7, 2, 2 = 142.' 



The carotid was left undamped for eight minutes, then clamped for one 

 minute, during which the chorda was stimulated. 



Saliva flow. 0, 0, 0, 2, 4, 6, 5, 5, 5, 4, 5, 4 = 40. 



The carotid was undamped, but the stimulus kept up for two minutes. 

 The blood flow from the vein was moderately increased. The saliva rose 

 69 and 51 mm. 



The carotid remaining undamped, the chorda was stimulated during the 

 third minute. It caused a rise of saliva of 203 mm. 



The effect of diminished blood supply upon the percentage composition 

 of saliva has not been very fully investigated. But Eckhard 2 states that 

 ligature of the veins of the submaxillary gland does not cause chorda 

 saliva to alter its character and become like sympathetic saliva. And, 

 according to Heidenhain, 3 diminution of the blood supply by compression 

 of the carotid does not cause an appreciable increase in the percentage of 

 solids in saliva. 



Heidenhain's experiments undoubtedly show that, in certain circum- 

 stances, a diminution of the blood supply to the gland has no considerable 

 influence upon the percentage of organic substance in the saliva, obtained 

 by stimulating the cranial nerve. But this does not seem to me to hold 

 in all circumstances, for, in some observations on the submaxillary 

 gland of the dog, made by Fletcher and myself, 4 bleeding the animal, 

 whilst decreasing the rate of the secretion of saliva produced by 

 pilocarpine, largely increased the percentage of organic substance in the 

 saliva. 



1 St'ud. d. physiol. Inst. zu Breslau, Leipzig, S. 93. 



2 Beitr. z. Anat. u. Physiol. (Eckhard), Giessen, 1860, Bd. ii. S. 212. 



3 Arch./, d. gcs. Physiol., Bonn, 1878, Bd. xvii. S. 33, 43. 



4 Phil. Trans., London, 1889, vol. clxxx. p. 131. 



