74 PHYSIOLOGY CHAP. 



has a temperature T5 C. higher than that of the arterial blood 

 which traverses the origin of the carotid. The difference in the 

 two temperatures is greater in proportion as the flow of saliva 

 from the cannula inserted in Whar ton's duct is more rapid 

 (C. Ludwig and A. Spiess). This proves that during secretion 

 the oxidative processes, or the respiration of the secretory cells 

 of the gland, increased so that much energy is liberated in 

 the form of heat. This is not contradicted by the fact first 

 noticed by Bernard to the effect that during the stimulation of 

 the chorda the blood flowing back from the gland assumes the hue 

 of arterial blood, because the velocity of the blood current in the 

 gland, owing to the vascular dilatation, increases more rapidly 

 than the consumption of oxygen. 



(/) The presence of oxygenated blood undoubtedly favours 

 secretion. If the principal vein that leaves the subniaxillary 

 gland be occluded while the chorda is stimulated, secretion gradu- 

 ally ceases, recommencing after the vein has been freed, with 

 sufficient lapse of time for the black asphyxial blood collected in 

 the vessels of the gland to be replaced by red arterial blood 

 (Ludwig). The rate of flow of saliva thus depends not only upon 

 the amount of nutritive materials that reach the gland, but also 

 upon the quantity of oxygen, i.e. the arterial character, of the 

 blood circulating in it. 



Barcroft (1901) noted in dogs that during the secretion pro- 

 duced by stimulation of the chorda the amount of oxygen taken 

 up by glandular tissue from the blood is three or four times 

 greater than in the resting gland. After injection of atropine 

 there is no longer any increased assimilation of oxygen on 

 stimulating the chorda, while more C0 2 is still given off, for a 

 time at any rate. 



(#) If the cranial and the sympathetic nerves of the sub- 

 maxillary are simultaneously excited, secretion is at first aug- 

 mented, but soon becomes slower than when one nerve alone 

 is stimulated, until finally it is almost entirely suspended 

 (Czermak). This effect is due to interference of excitation in the 

 two nerves, as well as to functional predominance of the con- 

 strictor fibres over the dilators in the nerves of the gland, as 

 shown by von Frey (see Vol. I. p. 351). 



(Ji) We have seen that secretion is arrested after section of 

 the chorda, even when the sympathetic is left uninjured. This 

 functional arrest is not permanent. After about 24 hours the 

 gland begins once more to pour out a continuous secretion of very 

 thin saliva, poor in organic substances. This phenomenon was 

 termed by Claude Bernard (who first noticed it) paralytic secretion. 

 It increases steadily in the first week : after that it slowly 

 diminishes, owing to the degeneration of the gland. After 

 excision of the subniaxillary ganglion (according to Bernard) 



