THE SECRETION OF SALIVA. 151 



activity of the salivary glands in one and the same way. Only in the case 

 of a f ew authors has the -state of dry ness of the food received mention as a 

 special factor in the case. But, as to the why and the wherefore of all this, 

 not one word, as a rule, is said ! One is led to suppose that the work 

 of the salivary glands is of no import, and that they respond in hap- 

 hazard fashion to every form of stimulus. Obviously the fruitful ideas 

 of the earlier authors had passed into complete oblivion. This could not 

 be ascribed to the occasional discrepancies in the observations of these 

 different authors, because, in spite of such, a kernel of truth always 

 remained. The utter inadequacy of any hypotheses to the contrary 

 must, however, be clear. How could it come about that the work 

 of the salivary glands should be robbed of its adaptation ? Where 

 is the reflex that could determine this, especially when we bear in 

 mind the accuracy of a sensation so finely differentiated as that presided 

 over by the nerves of taste ? In the case of the deeper-lying glands, 

 namely, those of the stomach and the pancreas, we had previously 

 learned many facts pointing indubitably to adaptation, and we could not 

 readily give our assent to the contrary representation. The experiments 

 concerning salivary secretion had, therefore, to be repeated.* 



We easily convinced ourselves that it was by no means the case that 

 every form of mechanical and thermal stimulus, without distinction, 

 excited a flow of saliva. Thus if a handful of small quartz pebbles be 

 thrown from a certain height into the dog's mouth, so that the mechanical 

 stimulus is fairly strong, the dog will gnaw them, move them backwards 

 and forwards, sometimes swallow a few of them, and yet no saliva flows, 

 or at most only one or two drops. Again, if ice-cold water be poured 

 into the mouth, or snow thrown in, no saliva will be seen. Obviously 

 it is not required in these cases. But cast in some sand, and the saliva 

 flows in quantities, because the sand cannot otherwise be got rid of 

 than by a free stream of fluid. Upon all substances which the clog 

 rejects for example, acids, salts, bitter and caustic substances saliva, 

 will likewise be poured, because these require to be neutralised, diluted, 

 or washed out of the buccal cavity. This explanation is fully confirmed 

 by the absolutely constant and striking fact that a thin watery saliva, 

 containing mere traces of mucin, is poured out by the mucous salivary 

 glands upon every substance, without exception, which requires to be 

 removed, while upon eatable substances a slimy mucin-holding fluid is 



* These experiments were begun by Dr. D. L. Glinski and afterwards continued 

 by Dr. S. H. Wulfson. They were performed on dogs in which the normal orifices of 

 the salivary ducts were displaced outwards. During the experiments a small 

 funnel (with a cylinder for collecting and measuring the saliva) was attached 

 to the skin around the orifice. The secretions of the sub-maxillary and sub-lingual 

 glands were jointly collected, that of the parotid separately. 



