It has indeed been alleged, that the ccecum is the seat of a special metamorphosis, which repeats, as it were, the process of gastric digestion:— that its mucous membrane pours out an acid secretion, which is capable of dis solving certain constituents of the food pre paratory to their absorption. But a closer examination dispels this view, and assigns to this segment an humbler office, which is closely analogous to that of the neighbouring portions of the canal. Its tubes, which have precisely the structure of those found else where, pour out an equally alkaline secretion. Its infusion, whether acidulated or otherwise, has no higher solvent power over albuminous substances than that possessed by the similar fluid prepared from pieces of ileum or colon. While the strongly acid reaction of its contents in many herbivorous animals is sufficiently explained as due to that lactic fermentation, which the various starchy substances are so apt to undergo when exposed to spontaneous decomposition at the temperature (about* 103°) of the intestinal canal. Consistently with su ch an explanation, this acid reaction is found chiefly or exclusively in those parts of the fiecal mass which are not in contact with the alkaline mucous membrane, and is by no means limited to the contents of the ccecal pouch.
We may therefore regard the fmces as com posed chiefly of two constituents :— which are derived, the one from the food taken by the animal, and the other, from the secretions of its digestive organs. And in like manner, we may premise what follows by stating, that the composition of any particular excre ment will always depend on the nature of the food, the state of the secretions, and the na ture and amount of the metamorphoses vihich both these constituents have together under gone.
Physical properties of the fceees— Subject to circumstances so numerous and fluctuating, it is obvious that the physical properties of the fmces must vary extremely in different sub jects. Their ordinary colour, odour, form, size, and consistence are so well known, as scarcely to require any special description in this essay.
As regards the two first of these characters, the contents of the small intestine are dis tinctly fmcal. But it is only in the ccecum, where both their colour and odour become much more marked, that the fmces usually begin to acquire a solid consistence. Their form and size is dictated, partly by the shape and diameter of the bowel (as already alluded + to), and partly by the degree in which their consistence has been augmented by the absorption of their watery parts. Where their solidity is much increased from this latter cause, the act of expulsion has little influence in modifying their form. The way
in which it usually does this has been previously pointed out.
The odour and colour peculiar to the fmces have been ascribed, by some authors, to the bile which enters into their composition ; by others, to the fluids which are poured out into the intestinal canal from the blood-vessels occupying its mucous membrane. It is, how ever, probable that they are not due to either of these causes exclusively', but depend rather on a combination of both; and are further mo dified by that admixture of altered (not to say decomposing) food, which forms so large a constituent of the excrement.
Thus, that they depend to some extent on the bile, is well shown by those cases of jaundice, in which a deficient secretion of this fluid, or an obstruction of its normal channel, has arrested its flow into the intestine. For in such instances, the ordinary brownish yel low tint, and fmcal smell, proper to the excre ment, are exchanged for a greyish white co lour, and an intensely putrefactive odour.
But it is certain that, unless the bile be poured out in excessive amount (as after the exhibition of mercury *), or conveyed through the bowels with unusual rapidity (as in diarrhcea and purging), it is but a small fraction of its total quantity that escapes re-absorption, so as to be found in the fmces. This statement especially applies to the meconium which occupies the intestine of the fcetus. At any rate, this substance contains but little of the acid or the colouring 'natter of ordinary bile.
Now, the preparation of excrement by the fcetus, and by hybernating or starving animals, is a satisfactory proof that its specific fmcal characters are not essentially due to any modifi cation of the alimentary matters contained in the intestinal canal. And since the bile forms but a small portion of its mass, it is evident that much of it must be derived from the se cretions of the digestive tube itself, and that its properties must be partially due to the same source. Indeed, this intestinal constituent, which is probably always a large ingredient of the fmces, becomes, in the hybernant and the fcetus by far the largest :— so much so, that the dried meconium contains about 85 to 95 per cent. of epithelium and mucus, al most all of which must be referred to this source. While, as regards its physiological import, it is impossible to doubt that it is (rar' Roy) v) the excrement :—that it is, in fact, the chief excretory ingredient of the fmces ; and hence that ingredient, the dismissal of which from the intestinal canal is most essen tial to the welfare of the organism generally.