DIGESTION.
18
of the agent to this purpose, has led to many
singular theoretical opinions, which will be
noticed in a subsequent part of this article*
But in whatever way, or upon whatever
principle we may explain the action of the
gastric fluid upon the aliment, we are irre¬
sistibly led to the conclusion, that it is the
physical agent which produces the effect, not
only from those cases, where in consequence
of a preternatural opening into the stomach
we are able to observe the actual phenomena
of digestion, but still more so, by the expe¬
riments on what has been termed artificial di¬
gestion, especially those of Spallanzani and
Beaumont, where the gastric juice has been
procured, and applied out of the stomach,
and where the process of chymification has
proceeded, as nearly resembling that in the
stomach itself as might reasonably be ex¬
pected, considering the unavoidable imper¬
fection of the experiment. This imperfection
respects both the mode of obtaining the gastric
juice itself, and the mode of applying it to
the aliment. We reduce the action of the
stomach into somewhat of an unnatural con¬
dition in order to procure the secretion, and
in the application of it we are deprived of the
contractile motion of the organ ; yet, not¬
withstanding these unavoidable circumstances,
the substances were reduced to a state very
considerably resembling that of chyme. That
this change was not produced by a mere me¬
chanical action is proved by the circumstance,
that the change in the substances operated on
bore no proportion to the hardness of their
texture or other physical properties. Thus we
find that the gastric fluid acts upon dense
membrane, and in some cases, even upon
bone, while there are other substances, of a
very delicate texture, which are not affected
by it. This kind of selection of certain sub¬
stances in preference to others bears so close
an analogy to the operation of chemical affinity,
that we ought not to refuse our assent to the
idea of their belonging to the same class of
tial agent in the process. From the first part of
this remark we must, however, except Yanhelmont
and Willis; Ortus Med. p. 164. .7 et alibi ; De
Ferment, op. t. i. p. 25. See Haller in Boerhaave,
Prælect. not. ad § 77, and El. Phys. xix. 1. 15,
and 4. 29 ; Fordyce, p. 150, 1 ; Spallanzani,
§ 239 .. 245 ; Hunter, p. 293 et seq. ; Circaud, ut
supra; Dumas, El. Phys. t. i. p. 278 .. 0 ; Tiede¬
mann et Gmelin, Recherches, t. i. p. 166,
7. It may be proper to remark that Leuret and
Lassaigne do not admit of the presence of this
acid ; they, on the contrary, suppose that the
gastric juice owes its acid properties to the lactic
acid ; Recherches Physiol, et Chimiques, p. 114. .7;
Dr. Prout has, however, as we conceive, satisfac¬
torily answered their objections to his experiments ;
Ann. Phil. v. xii. p. 406. Dr. Carswell considers
acidity to be the essential and active property
of the gastric juice ; Pathol. Anat. fas. 5.
* Montegre has lately performed a series of ex¬
periments, the results of which lead him to deny
the specific action of the gastric juice ; Expér. sur
la Digestion, p. 43, 4. But, notwithstanding the
apparent accuracy with which they were conducted,
we cannot but suspect some source of error, seeing
how much they are at variance with all our other
information on the subject.
actions, although it occurs under circum¬
stances where we might not have expected to
find it.
There are two other properties of the gastric
juice, besides its solvent power, which are at
least as difficult to account for, but of which
we seem to have very complete evidence,—
its property of coagulating albumen, and that
of preventing putrefaction. It is the former
of these properties which we employ in mak¬
ing cheese, cheese being essentially the albu¬
minous part of milk, coagulated by means of
what is termed rennet, a fluid consisting of the
infusion of the digestive stomach of the calf.
This is unequivocally a chemical change, yet
it is very difficult to explain it upon any che¬
mical principle, i. e. to refer this individual
case to any series of facts, with which it can
be connected.* We can only say in this
instance, as in so many others in the physical
sciences, that although the fact is clearly
ascertained, its efficient cause still remains
doubtful.
We are compelled to make the same re¬
mark with regard to the other property of the
gastric juice, to which we have referred above,
its antiseptic power. Of the fact, however,
we are well assured, both as occurring in the
natural process of digestion, and in the expe¬
riments that have been made out of the body.
It is not uncommon for carnivorous animals
to take their food in a half putrid state, when
it is found that the first action of the gastric
juice is to remove the fcetor; and an effect of
precisely the same kind was noticed by Spal¬
lanzani in his experiments.-! Here again we
have a chemical change, the nature of which
we cannot explain; it is, however, a circum¬
stance which may appear less remarkable, with
respect to the subject now under consideration,
because the action of antiseptics generally is
one which we find it difficult to refer to any
general principles.
Respecting the process of chymification it
only remains for us to remark, that the con¬
tractile action of the stomach is admirably
fitted to aid the chemical action of the secreted
fluids ; the vermicular motion of the organ has
the effect of keeping the whole of its contents
in a gradual state of progression from the
cardia to the pylorus, while, at the same time,
each individual portion of the aliment is com¬
pletely mixed together, and brought into the
* This difficulty appears to be increased by the
amount of effect which is produced by the very
small quantity of the agent ; Fordyce informs us,
that a very few grains of the inner coat of the
stomach, a very small proportion of which must
have consisted of the secretion, was capable, when
infused in water, of coagulating more than one
hundred parts of milk; p. 57,9; 176 et seq.;
Prout, Ann. Phil. v. xiii. p. 13 et seq.
t Expér. § 250..2 et alibi ; see also Hunter on the
Anim. Œcon. p. 204. Montegre does not admit
of this property, and would appear to doubt also
of the coagulating power of the gastric juice, p. 21
et alibi ; the same opinion is also maintained hy
Dr. Thackrah, lect. p. 14; but it would require a
very powerful series of negative facts to controvert
the strong evidence that we possess on this
subject.