490 THE SALIVARY GLANDS. 
\\\ 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 
Schitf 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 1 icing 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 bodies. 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: latter 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 cannulse 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 effect on the several glands was practically the same with 
all the substances. 
Schitf 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, 15 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. comparer," 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 " Lecons sur la physiologie de la digestion," 1867. 
3 Colin and Prompt (1874), case of parotid fistula (cf. supra). 
4 " Lecons de physiol. exper.," lSr>6, tome ii. p. 82. 
5 " Lecons sur la physiol. de la digestion,"' 1867, tome i. p. 1S6. 
6 Op. cit., p. 653. 
