5 1 6 THE SALIVAR Y GLANDS. 
On the hypothesis that nicotine causes a contraction of the terminal 
fibrils of the chorda tympani, we might suppose that protracted stimulation 
leads to a slow gradual extension of the terminal fibrils, so that nervous 
impulses passing down the chorda tympani can again set up impulses in the 
peripheral nerve-cells. 
Formation or Heat in the Submaxillary Gland. 
The rapid flow of saliva caused by stimulating the chorda tympani 
suggested, not unnaturally, that a considerable formation of heat must 
take place in the submaxillary gland. Ludwig and Spiess, 1 using thermo- 
electric junctions, and Ludwig, 2 using thermometers specially designed, 
brought experimental proof that in the dog this was in fact the case. 
Ludwig and Spiess placed one junction in the carotid artery, 
arranged as in the method of determining lateral blood pressure, so 
that the actual junction w T as, they said, in the full blood stream. The 
other junction was placed in a cannula connected with Wharton's 
duct, and apparently on the same side as that of the carotid taken. 
With a moderate rate of secretion they found the saliva to be about 
1° C. warmer than the blood in the carotid. 
Ludwig placed one thermometer in the carotid near its origin, and 
another in the course of a cannula connected with Wharton's duct of the 
opposite side. He states that there was in no case clotting in the 
carotid, but there does not seem to have been a flow of blood around the 
bulb of the thermometer. The room was kept at a temperature not 
less than 24° 0. The saliva was found to be constantly of a higher 
temperature than the blood. The extent of this varied in different 
experiments, and, generally speaking, was greater the faster the secretion. 
The maximum difference found was 1 0, 6 C, the temperature of the saliva 
in this case being 41 0, 2 C, the rate of secretion 05 c.c. in 5 - 5 seconds. 
Ludwig gives also three experiments upon the respective temperatures of 
the blood in the carotid artery, of the blood issuing from the gland vein, 
and of the saliva. As a rule, the temperature of the venous blood was 
below that of the carotid blood, but occasionally it was slightly greater 
than that of carotid blood or of saliva. For example, in one case the 
temperature of the blood in the carotid was 39°'l (1, that of the saliva 
39°"3 C, and that of the venous blood 39 0, 4 C. 
The proof of an appreciable formation of heat during secretion 
appeared complete when Heidenhain 3 observed by the thermo-electric 
method that the temperature of the gland was often higher than that 
of the carotid blood, the difference in favour of the gland being still 
greater on stimulation of the sympathetic ; and wdien Morat, 4 by the 
same method, obtained a rise of temperature in the submaxillary gland 
of the dog, on stimulating the sympathetic both after bleeding the 
animal to death and during temporary ligature of the carotid, sub- 
clavian, and vertebral arteries. 
Bernard 5 plunged one thermo-electric junction needle in each gland, and 
found that stimulation of the chorda tympani caused a rise of temperature, and 
1 Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1S57, Bd. xxv. S. 584 ; reprinted in 
Ztschr.f. rat. Med., 1858, X. F., Bd. ii. S. 361. 
2 Wien. med. Wchnschr., I860, S. 433 and 449. 
3 Stucl. d. physial. Inst, zu Breslaib, Leipzig, 1868, Heft 4, S. 110. 
4 Arch, de physiol. norm, et path., Paris, 1893, p. 285. 
5 "La chaleur auimale," Paris, 1876, p. 325. 
