INFLUENCE OF NERVOUS SYSTEM ON DIGESTIVE GLANDS 397 



chorda tympani is stimulated with currents of varying strength, 

 the quantity of organic substances in small samples of saliva 

 collected from a fresh gland is more nearly proportional to the rate 

 of secretion than is the quantity of water and salts, which varies 

 also with the blood-supply. 



Lest the apparently insignificant result of artificial stimulation 

 of the sympathetic in such animals as the dog should cause its 

 secretory action to be aopraised at too low a value, it should be 

 remembered that in me intact body the sympathetic secretory fibres, 

 when they are excited, are, it may be assumed, excited independently 

 of the vaso-constrictors, and even in conjunction with the vaso- 

 dilators' of the salivary glands. 



It is conceivable that such differences between chorda and 

 sympathetic saliva as are not accounted for by the differences in 

 the blood-flow during their stimulation are due, not to the nerve 

 fibres, but to the end organs with which they are connected; that 

 is, the two nerves may supply, not the same, but different gland- 

 cells. And it is well known that even after prolonged stimulation 

 of the chorda or chordo-lingual alone, some alveoli of the dog's 

 submaxillary gland remain in the ' resting ' state ; after stimulation 

 of the sympathetic alone, the number of unaffected alveoli is much 

 greater; while after stimulation of both nerves, few alveoli seem 

 to have escaped change. If there is no essential difference between 

 the cranial and sympathetic secretory fibres, it is easy to understand 

 that they will be distributed to different secreting elements. The 

 supposed proof that there must be some overlapping in the nerve- 

 supply i.e., that some cells must be supplied from both sources, 

 since excitation of the sympathetic influences the amount of organic 

 material in the saliva obtained by subsequent stimulation of the 

 chorda is, as we have just seen, by no means so cogent as has been 

 assumed. And, indeed, we know nothing of a division of labour 

 between the cells of a gland, except when there are obvious anatom- 

 ical distinctions. Thus, the submaxillary gland in man contains 

 both serous and mucous acini, and mucin-making cells are scattered 

 over the ducts of most glands, and, indeed, on nearly every surface 

 which is clad with columnar epithelium. In these cases we cannot 

 doubt that one constituent mucin of the entire secretion is manu- 

 factured by a portion only of the cells. In the cardiac glands of the 

 stomach, too, the ovoid cells, in all probability, yield the whole of 

 the acid of the gastric juice. But, so far as we know, every hepatic 

 cell is a liver in little. Every cell secretes fully-formed bile ; every 

 cell stores up, or may store up, glycogen. So it is with the secretory 

 alveoli of the pancreas, if we consider the islands of Langerhans as 

 having no connection with the alveoli; one cell is just like another; 

 all apparently perform the same work; each is a unicellular pan- 

 creas. (See p. 638.) 



Paralytic Secretion. When the chorda tympani is divided, a slow 

 ' paralytic ' secretion from the submaxillary gland begins in a few 



