494 THE SALIVAS. Y GLANDS. 
soon becomes slow or stops altogether, but, on cutting off the rapid shocks 
from the upper electrodes, the stimuli at the lower electrodes become again 
effective, and the secretion starts once more. The results are similar to those 
he obtains with motor nerves to skeletal muscle. 
The real latent period of the gland cells cannot be accurately deter- 
mined by any direct method, and in consequence it is customary to speak 
of the interval between the moment of stimulating the nerve, and the 
moment at which the movement of saliva occurs in the duct, as the 
latent period. When the cranial nerve is stimulated with a weak 
current, there is an obvious interval — usually two to four seconds — 
between the moment of application of the stimulus and the appear- 
ance of saliva in the cannula, and this is the case although the 
secretion when it occurs is not scanty. When stronger currents are 
used, and the secretion is copious, the latent period is much dimin- 
ished. On the other hand, when the secretion is scanty, the latent 
period is very much prolonged, whatever the strength of current ; thus, 
after a small dose of atropine, it may lie half a minute or even more. 
The percentage of organic substance in saliva obtained from differ- 
ent salivary glands varies considerably; in each, as we shall see, it 
varies in different circumstances, and in each it may be small (0 - 2 
to 0'5 per cent.). But, other things being equal, the submaxillary 
saliva has usually a higher percentage of organic substance than 
either the sublingual or the parotid saliva. 
There is a curious difference in the percentage of salts found in 
different salivas. In the dog the maximum percentage of salts in the 
parotid saliva is about 068, in that of the submaxillary gland about 
077, and in that of the sublingual gland about TO. 1 In the rabbit 
the parotid saliva has a maximum percentage of about 0*85. 2 
After action of a strong stimulus.— Strong stimulation of the 
cranial nerve alters the gland it supplies in such a way, that the 
saliva secreted shortly afterwards has a higher percentage of solids 
than it otherwise would have had. 3 Thus, in the experiment quoted 
on p. 501, the first weak stimulation of the chorda tympani caused 
secretion of a saliva containing 0*52 per cent, of organic substance, 
whilst, after a strong stimulation, a second weak one caused a secre- 
tion having a percentage of TOT of organic substance. 
This, however, only holds when successive small quantities of 
saliva are collected; with larger quantities, as 10 c.c. to 12 c.c, 
no such after action is observed (Werther). 
Stimulation of the Sympathetic Nerve supplying a 
Salivary Gland. 
Ludwig 4 (in 1856) discovered the secretory power of the sym- 
pathetic; he obtained a secretion from the submaxillary gland of 
the dog, by stimulating both the cervical sympathetic and the nerve 
filaments on the gland artery. 
1 Werther, Arch. f. d. ges. Physiol., Bonn, 1886, Bd. xxxviii. S. 293 ; Langley and 
Fletcher, Phil. Trans., London, 1889, vol. clxxx. p. 109. 
2 Heidenhain, Arch. f. d. gcs. Physiol., Bonn, 1878, Bd. xvii. S. 40. 
3 Heidenhain, 075. cit., 1878. 
4 Quoted by Czermak, Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1857, Bd. xxv. S. 3 ; 
Czermak also obtained secretion on stimulating the cervical sympathetic. 
