490 THE SALIVARY GLANDS. 



In man during hunger, the sight, smell, or idea of food is sufficient 

 to cause a secretion of saliva from all the salivary glands ; and 

 chewing insoluble substances has a similar, though apparently a less 

 effect. 1 



Secretion in this way is said not to occur in lower animals. Thus 

 Schiff 2 found in a dog with a parotid fistula, that no flow of parotid 

 saliva was caused by the sight or smell of the meat the animal was 

 endeavouring to obtain ; when it was induced to bite a piece of wood, 

 the meat still being in sight, there was slight secretion from the 

 submaxillary gland but none from the parotid, but on placing sapid 

 substances in the mouth there was at once a rapid secretion. And Colin 

 states that, after a parotid fistula has been established in a horse, and 

 when the animal is in a state of hunger, there is no secretion from the 

 parotid when the animal is offered, but not allowed to take, corn, nor 

 when it masticates oakum, although mastication of corn readily causes 

 a secretion. 



Sapid substances taken into the mouth cause more or less secretion 

 from all the salivary glands. In man all substances are effective, and 

 drinking, wine for example, is sufficient. 3 Acid placed on the tongue is 

 apparently the most effective stimulant among the sapid substances, but 

 there are not sufficient observations in man as to the amount of saliva 

 produced by other substances, to allow a satisfactory opinion to be formed 

 as to the relative effectiveness of salt, sweet, and bitter 1 todies. Masti- 

 cation considerably increases the flow of saliva, probably by bringing 

 the particles into better and more frequent contact with the mucous 

 membrane. 



Chloroform and ether when inhaled cause secretion, by stimulating 

 the gustatory nerve endings, and possibly also the other nerve-endings in 

 the mucous membranes; if given by the trachea, they do not cause 

 secretion. Alcohol, ether, or chloroform, when mixed with water and 

 held in the mouth, cause a fairly free secretion of saliva. 



In carnivora, so far as the experiments go, acids (vinegar, tartaric 

 acid) cause the most abundant secretion ; salts, either neutral or alka- 

 line, a less secretion, but still a fairly copious one ; bitter substances a 

 much less secretion, and sugar little or even none. With sapid sub- 

 stances in the mouth the secretion is increased by mastication. 



Thus Bernard, 4 in one experiment on a dog, in which eannulae were placed 

 in the ducts of all three glands, obtained a copious secretion from vinegar, less 

 from sodium carbonate, still less from colocynth, and none from sugar or from 

 water. The relative elfect on the several glands was practically the same with 

 all the substances. 



Schirf 5 obtained some secretion from the parotid fistula of a dog by 

 placing sugar on the base of the tongue, but none by placing it on the tip. 



According to Colin, 6 weak acids, salts, or aromatic substances placed on 

 the buccal mucous membrane give rise to no appreciable secretion from the 

 parotid of the horse during abstinence, and do not sensibly increase the con- 



1 Colin and Prompt, 1874 (see Colin, "Traite de physiol. comparee," etc., 3rd edition, 

 p. 1), in the case of a girl with a parotid fistula, noticed that chewing a piece of ribbon 

 caused a secretion of only one drop of saliva in two minutes. 



2 " Lemons sur la physiologic de la digestion," 1867. 



3 Colin and Prompt (1874), case of parotid fistula (cf. supra}. 



4 "Lemons dc physiol. exper.," 1856, tome ii. p. 82. 



5 " Le9ons sur la physiol. de la digestion,'' 1867, tome i. p. 186. 

 0p. cit., p. 653. 



