494 THE SALIVAR 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 scant^. 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 be 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 (O2 

 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 clog the maximum percentage of salts in the 

 parotid saliva is about 0'6S, in that of the submaxillary gland about 

 0'77, and in that of the sublingual gland about I'O. 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 lias 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 1/07 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. ges. PhysioL, Bonn, 1878, Bd. xvii. S. 40. 



3 Heidenhain, op. cit., 1878, 



4 Quoted by Czermak, Sitzunysb. d. k. AJcad. d. JVissensch. , Wien, 1857, Bd. xxv. S. 3 ; 

 Czermak also obtained secretion on stimulating the cervical sympathetic. 



