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.