DIETETICS, 
slastn of alchemy, which raged in his time, 
attributed digestion to the vital energy of 
the soul, which resided, as he thought, in 
the stomach, 
Grew and Santarelli were of opinion, 
that the spirits wliich are poured forth from 
the nerves of the stomach, sei-ved for the 
concoction of the food. Boerhaave, who 
has in reality only attempted to reconcile 
the variety of opinions that had been pro- 
posed before him, supposes tliere are two 
principal agents in this vital function, viz. 
the different fluids that are collected in the 
stomach, and the mechanical action of that 
organ ; the secondary agents, according to 
him, are heat, air, the nervous fluid, the re-, 
mains of the food, and an incipient fermen- 
tation, opposing it m the extensive sense in 
which it w as considered before him. With 
respect to the gastric fluid, his ideas appear- 
to be indeterminate, and unsettled ; he, 
however, conceived that its action on the 
food was merely as a simple diluent, like 
water, when heated to the same tempera- 
ture. He had no suspieicn of its being a 
solvent, or that it was capable of acting 
upon tire more tenacious and hard sub- 
stances that were taken in as food. Ac- 
cording to Pringle and Macbride, diges- 
tion is carried on by a complete fermenta- 
tive process. The food divided by masti- 
cation, and peiietrated by the saliva, begins 
as soon as it enters the stomach, to be agi- 
tated by that intestine motion which alw'ays 
accompanies .feiTOentation ; this motion is 
excited by the wannth of that viscus, by 
the old remnants of the food, by the gastric 
fluid, and more particularly by the saliva,^ 
which is above all adapted to produce and 
promote this process. They supposed that 
the first effect of this intestine commotion 
is to raise the solid parts of the aliment to 
tlie surface of the gastric liquor, where they 
will be for some time sustained by the air 
bubbles, which, on thpir ceasing, must fell 
down again, and be thoroughly incorpo- 
rated with the fluids of the stomach. This 
mixture is rendered still more complete by 
the peristaltic motion, the alternate pres- 
sure of the diaphragm and abdominal mus- 
cles, and the continual pulsation of the ad- 
jacent large vessels : in this state the food 
passes into the small intestines, where the 
fermentative motion prqduces still greater 
changes by the assistance of the bile and 
pancreatic juices ; it is then converted into 
chyle. According to Ihe opinion of Haller, 
the gastric juice is more or less acid in dif- 
ferent animals j its action on the food very 
much resembles that of water, in which a 
little salt has been dissolved, which, from 
experience, is known to possess a very 
great resolvent power ; and the consequence 
is, that an incipient fermentation takes 
place which reduces the aliments to a pul- 
taceous mass. In animals that feed on 
seeds, this process is assisted by trituration, 
These, with many other fanciful opinions, 
took place in their turn, when Cheselden 
by chance happened to conjecture right, 
viz. that digestion was performed by some 
unknown menstruum. This conjecture was 
confirmed by Reaumur and Spallanzani, 
who have proved the menstruum to be the 
gastric juice, by a number of experiments, 
a general view of which it will be neces- 
sary to give, 
Spallanzani made his experiments by in- 
troducing certain substances, such as raw ve- 
getables, &c. enclosed in small perforated 
tubes, and causing animals to swallow them j 
he then either destroyed the animal, in or- 
order to examine it, or waited until it 
was vomited up. The animal kingdom may 
be divided into three kinds; containing 
stomachs muscular, intermediate, or mem- 
branous; the last class is infinitely more 
numerous than the two former. Of ani- 
mals with muscular stomachs, such as fowls, 
turkeys, ducks, geese, doves, pigeons, &c. 
fhe food is seeds, such as wheat, barley, 
pease, ike. ; when it is taken spontaneously 
by these bird% it remains sometime in the 
craw, where it is macerated and becomes 
softer ; it is then conveyed into the sto- 
mach or gizzard, vyhich is composed of very 
strong muscles, capable of grinding not only 
the grain it receives, but is of such force as 
even to reduce small pieces of glass, and 
blunt the points of needles : by this means 
the food is triturated and reduced very 
small 5 it is then converted, by the gastric 
juice it meets with in this viscus, into a pul- 
taceous mass called chyme. Spallanzani 
found, that the gastric juice of this class di- 
gests flesh, and that the animals are for the 
most part both frugivorous and granivorous. 
He found it dissolved raw flesh, when 
bruised, in about two days ; hut yvhen en- 
tire, four and sometimes five days were ne- 
cessary : it dissolves grain only when 
bruised ; hence, in the gallinaceous class, 
trituration and the gastric fluid in the giz- 
zard, although Reaumur was of opinion it 
contained no menstruum, mutually assist 
each other ; the former by breaking down 
the aliments in a mechanical way, prepares 
it for the latter, which penetrates it, de- 
