EFFECT OF VARIATIONS IN THE BIOOD 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 tar compressed that little blood Mows 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 flotv.—O, 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 flou:—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.— O, 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 Stud. d. physiol. Inst, zu Breslau, Leipzig, S. 93. 
2 Beitr. z. Anat. u. Physiol. (Eckhard), Giessen, 1860, Bd. ii. S. 212. 
3 Arch./, d. ges. Physiol., Bonn, 1878, Bd. xvii. S. 33, 43. 
4 Phil. Trans., London, 18S9, vol. clxxx. p. 131. 
