DIGESTION IN THE MOUTH 



747 



composition of sub-inaxillary saliva obtained by weak and strong 

 stimulation of the chorda tympani nerve : 



With the strong stimulus the amount of saliva was increased 

 over fourfold, while the percentage of organic substances in the 

 saliva was raised from 0-84 to 2-06 per cent. There was at the same 

 time an increase in the percentage of salts. If the excitation be 

 continued for a considerable time, there is a gradual rise in the per- 

 centage of inorganic salts and a fall in the percentage of organic matter. 



The cranial nerves going to these glands have another important 

 effect, namely, vaso-dilatation. It was shown by Claude Bernard 

 that if the outflow from the vein of the sub-maxillary gland were 

 measured, on exciting the chorda tympani the flow might increase 

 four to eight times, and indeed to such an extent that the blood 

 passing through the gland did not stay there long enough to lose its 

 oxygen. Moreover the dilatation of the arterioles removes the 

 normal resistance which serves to damp and obliterate the pulse 

 between the arteries and the veins. As the result of exciting the 

 chorda therefore the blood coming from the vein may show distinct 

 pulsation, and may have a brilliant scarlet hue just as if it were 

 derived from an artery. The same dilatation has been observed to 

 attend excitation of the cranial supply to the parotid gland. 



The effects of exciting the sympathetic nerve supply differ according 

 to the gland and the animal which is the subject of experiment. 

 In the dog excitation of the cervical sympathetic causes the secretion 

 of a few drops of thick viscid saliva from the sub-maxillary gland. 

 In this animal no secretion is obtained at all from the parotid 

 gland on exciting the sympathetic, but the influence of the excita- 

 tion is shown by the occurrence of histological changes in the 

 gland-cells. In the cat the sub-maxillary saliva obtained on sym- 

 pathetic excitation may be as copious as and even more watery 

 than the saliva obtained from the sub-maxillary on stimulation 

 of the chorda tympani. We shall have later on to discuss how far 

 these results are to be ascribed to a fundamental difference in the 

 point of attack of impulses carried to the secreting cells by the two 

 sets of nerve fibres, and how far to the varying effects of the cranial 

 and sympathetic nerves respectively on the blood-vessels. It must 



