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 OF HEAT IN THE SUBMAXILLAKY 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 was, 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 C. 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 1'6 C., the temperature of the saliva 

 in this case being 41'2 C., the rate of secretion 0-5 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 w r as 

 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 391 C., 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 when 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, 1857, Bd. xxv. S. 584 ; reprinted in 

 Ztschr.f. rat. Med., 1858, N. F., Bd. ii. S. 361. 



2 Wien. med. Wchnschr., I860, S. 433 and 449. 



s Stud. d. physiol. Inst. zu Breslau, Leipzig, 1868, Heft 4, S. 110. 



4 Arch, de physiol. norm, et path., Paris, 1893, p. 285. 



5 "La chaleur auiraale," Paris, 1876, p. 325. 



