914 THE EXTERNAL SECRETIONS 



terial as that obtained with the aid of the acid. What is true of the 

 submaxillary must also be true of the other glands ; but naturally, these 

 differences cannot be detected so readily directly within the mouth, 

 because all three secretions are poured into this common reservoir at 

 one time. It is also of interest to note that the daily amount of saliva 

 furnished by each gland exceeds its weight ten or twelve times. The 

 total production of these glands, therefore, cannot be less than one 

 liter, this quantity including the small portion which is poured forth 

 constantly to moisten the surfaces of the mouth as well as those 

 extra amounts which are produced from time to time in response to 

 stimulations. 



The facts which may be mentioned in explanation of these funda- 

 mental differences in the saliva, must necessarily be of a very general 

 kind, because they are based upon the still very obscure microphysical 

 and microchemical occurrences in cells. Thus, it may be assumed that 

 the nerves innervating the salivary glands are capable of conveying 

 impulses of different kinds or that each nerve contains separate sets 

 of fibers which react specifically to different stimuli. 1 This assump- 

 tion finds substantiation in the fact that the action of the cerebral 

 (parasympathetic) nerve is quite different from that of the sympa- 

 thetic nerve. To illustrate, if the chorda tympani is stimulated, it 

 will be found that the submaxillary gland reddens and becomes 

 warmer to the touch, because its blood-vessels are markedly dilated. 2 

 It may then also be observed that the blood returned from this 

 gland possesses a much brighter color, and that the small vein draining 

 it pulsates markedly. These pulsations are due to the arterial pulse 

 which is propagated at this time directly through the dilated and 

 non-resistant capillaries. Contrariwise, the excitation of the cervical 

 sympathetic nerve causes this gland to become pale, to decrease in 

 volume, and to become distinctly cooler to the touch. These changes 

 unmistakably point to alterations in its blood-supply, the excitation 

 of the chorda tympani giving rise to vaso-dilatation and the stimula- 

 tion of the sympathetic fibers to vaso-constriction. 3 



Curiously enough, these changes in the vascularity of this gland 

 are associated with very decided changes in the quantity and quality 

 of the saliva. 4 Very soon after the beginning of the stimulation of 

 the chorda tympani, Wharton's duct becomes highly distended and 

 discharges a quantity of saliva four or five times larger than normal. 

 The secretion itself is very watery and possesses only a slight viscidity. 

 It contains no more than 1 or 2 per cent, of total solids. If a suffi- 

 ciently long interval is allowed to separate the successive stimulations, 



1 Pawlow, Ergebn. der Physiol., iii, 1905. 



2 Cl. Bernard, Compt. rend., 1858. 



3 These differences may also be recognized by means of the stromuhr or current 

 measurer. See: Burton-Opitz, Jour, of Physiol., xxx, 1903, 132. 



4 First observed by Ludwig, Arbeiten aus dem physiol. Institut zu Leipzig, 

 1851. 



