184 PHYSIOLOGY OF ALIMENTATION. 



its descent through the oesophagus, is s< Dieted. Still, 

 great care must be exercised in looking upon every re- 

 action of an organism, or one of its organs as eminently pur- 

 poseful (as does PAWLOW 1 ), and therefore for the ultimate 

 good of the organism. We are familiar with too many illus- 

 trations of the fact that living matter may possess character- 

 istics that are eminently dangerous to its life and well-being. 



Of much interest is the connection between the physi- 

 ology and what may be called the psychology of the salivary 

 glands. We see in the facts about to be discussed a strik- 

 ing illustration of how the organic functions of an organ may 

 be markedly influenced through the state of the mind an 

 illustration not without interest to the clinicist. The same 

 series of reactions can be obtained as have been described 

 above, when the animal's attention is simply directed to the 

 substances in question. When the experimenter simply pre- 

 tends to throw pebbles or snow into the mouth of the dog no 

 secretion follows, but the saliva flows copiously if sand takes 

 the place of the pebbles. If various kinds of food are offered 

 the animal, saliva flows or not, just as though the animal had 

 been really feed them. Moreover, the same qualitative varia- 

 tions are noted in the saliva. If the proffered food is dry, 

 much watery saliva is secreted, while a slimy saliva less in 

 amount is poured out when meat is offered. 



Brief mention must now be made of the paths over which 

 impulses travel to the cranial and sympathetic nerve fibres 

 which supply the salivary glands and influence their secre- 

 tions. Both these sets of nerve fibres originate from the 

 medulla or in the pons and spinal cord just above and below 

 this. CLAUDE BERNARD'S experiments are therefore of great 

 interest, which show that injury to certain portions of the 

 medulla causes a copious flow of saliva. Whatever means 

 be employed in bringing about a reflex secretion of saliva, 

 this can only be possible through impulses passing from 



J See PAWLOW: Work of the Digestive Glands, Translated by 

 THOMPSON, London, 1902, pp. 151 and 152, 



