PHYSIOLOGY, 
^fftty years. Many men live only on certain 
'Vegetables, as potatoes, chesnuts, dates, &c. 
sSorae wandering Moors, according to Adam- 
son, live almost entirely on gum Senegal. 
Fish is the only food of numerous unciviliz- 
ed tribes on different coasts : and flesh of 
others. Some barbarous hordes stilt eat 
raw meat, and even the human body some- 
times serves them as a repast. In several 
islands between the tropics, particularly in 
the South Sea, there is no fresh water, and 
the milk of the cocoa-nut is used instead : 
various other singular facts relating to the 
food and drink of man might be collected 
Iiere, showing very clearly that he is an om- 
nivorous animal. 
Whatever be the diversity of food, the 
action of our organs always separates the 
same nutritive principle from it: in fact, 
let the diet be totally vegetable, or totally 
animal, the peculiar composition of our 
organs does not alter, an evident proof that 
the matter we extract from aliment to ap- 
propriate to ourselves is always alike. 
It has been a matter of dispute vdiether 
pure water furnish any nourishment, or be 
a mere diluent. 
We have nothing further to say concern- 
ing the processes of mastication and deglu- 
tition, than what the reader will find in the 
article Anatomy, under the head of “ Or- 
gans of Mastication and Deglutition.” 
Salivary Secretion, This has been esti- 
mated by Nuck at the quantity of one pint 
in twenty-four hours. Although it probably 
goes on to a certain degree at all times, yet 
it is more copious when we take foo^; and 
the augmentation of quantity arises partly 
from stimulus, partly from mechanical pres- 
sure. When any acrid matter is taken into 
the mouth, an increased flow of saliva is 
produced ; and this may also follow the 
mere sight of food, and hence has arisen 
the well-known expression of the “ mouth 
watering.” 
All the salivary glands are so situated 
that the motions of the jaw, and other in- 
struments of mastication, necessarily sub- 
jects them to considerable pressure, by 
which their secretory tubes are evacuated, 
and new secretion promoted. 
The saliva is conveyed into the mouth by 
•the contractile power of the salivary duct's, 
which, in some rare instances, are said to 
have projected it even from the cavity of 
the mouth. The great number of vessels 
and, nerves which belong to, and are pla- 
ced near these glands, correspond to the 
copious supplies of fluid which they furnish. 
Besides the simple water furnished by 
the true salivary glandsj the mucous fol- 
licles, which abound on the surface of the 
mouth, supply a considerable proportion of 
that fluid to be mixed with the food. These 
additions being, by means of mastication, 
intimately blended with the food, not only 
reduce it to a soft pultaceous mass, more 
fit for the process of deglutition, but also 
bring it into a state of convenient prepara- 
tion for the subsequent process of digestion 
and assimilation. In this pqipt of view 
mastication is very important, as we may 
observe from the ill effects which ensue 
when the loss of the teeth renders it imper- 
fect in old persons. 
For the chemical analysis of Saliva, the 
reader will look to that word ; and for an 
account of the digestive process itself, to 
the article Dietetics; in which are also 
several observations respecting food. 
While the dissolution of the food, pro- 
duced by the solvent action of the gastric 
juice, is going on, the two orifices of the 
stomach remain accurately closed. No gas 
ascends through the oesophagus, except 
when the digestive process is imperfect. 
Soon the muscular fibres of the organ begin 
to act : the circular ones, contracting at 
first in a vague and oscillatory manner, soon 
act more uniformly from above downwards, 
and from right to left; that is, from the 
oesophagus to the pylorus ; while the lopgi- 
tudinal part approximates the two openings. 
The pylorus seems to possess a peculiar 
and exquisite sensibility, by which it dis- 
tinguishes whether the substances brought 
in contact with it have been sufficiently 
acted on by the gastric juice ; if that is the 
case, it releases and allows them to pass, 
while it remains closely contracted against 
those which are not thoroughly digested. 
The time occupied by the digestive pro- 
cess must be expected to vary according to 
the constitution, age, and health of the in- 
dividual, and the nature of the aliment ; 
but it may be stated, in general, at four 
hours. 
The action of the stomach is sometimes 
inverted, and the contractiohs, which in that 
case are forcible, rapid, and convulsive, 
cause vomiting. The exertions of the res- 
piratory muscles are, however, necessary to 
the production of this eflfect. 
Although the stomach belongs to those 
organs whose action is independent of the 
will, and goes on therefore witliout the at- 
traction of the individual, yet it is so far in- 
fluenced by the brain, that the section of 
