In any case, unless we suppose the capil laries of the intestine to be the actual site of an unexampled generation of gas from the con stituents of the blood, an inquiry into these latter will probably afford us some grounds on which to accept or reject the above theory.
It is therefore important to point out, that some of the gases found in these analyses — viz. hydrogen, carburetted hydrogen, and sul phuretted hydrogen — have never yet been detected in any appreciable quantity in the blood. And hence without assuming their complete absence from this liquid, we may at least infer that they are not present in that amount which would be necessary to explain their secretion from it, to the extent men tioned in these observations.
To this we may add, that no parallel to such a process of gaseous excretion can be observed in the case of any other vascular surface. This statement not only holds good of the serous membranes, but (what is much more conclusive) even of those structures which are specially organized with reference to the giving out from the blood of certain of its gases, and the taking up of others from the surrounding air. It is to the skin and lungs that we should naturally look for evidence of the true secretion of excrementitious or noxious gases from the circulating fluid. And yet, on turning to the results afforded by the eudiometric researches of a number of ob servers, we find that the gases which we have just stated to be absent from the blood, are equally deficient in the air exhaled from the vessels of these special organs of gaseous excretion. While even the carbonic acid and nitrogen of the intestinal flatus are at once distinguished, by their quantitative relations, from the same gases, as found in the air of expiration. Thus the minute amount of nitrogen in the air exhaled from the lungs is contrasted with an average of 40 per cent. in the gases contained in the intestines; and its proportion to the carbonic acid present, is increased from T-6-uth in the former, to id, or even tths, in the latter gaseous mixture, In conclusion, we may point out, that while the carbtiretted and sulphuretted hydrogen, as well as the pure hydrogen, of these analyses, can only be explained as the result of a pro cess which directly or indirectly involves the deoxidation of water,— the chemistry of the organism seems always to reverse this process. Far from deoxidating this liquid, there are good grounds for supposing that a quantity of water amounting to nearly ith of the whole aqueous contents of the food is daily formed in the body by a combustion (or in other words, by an oxidation) of the hydrogen of its tissues.
But some will perhaps think that these con siderations are sufficiently answered by facts, which deserve more reliance than any such arguments.
They would possibly instance experiments like those made by Magendie* and Girardin, and confirmed by Frerichs+ : in which the de ligation of an empty portion of intestine had nevertheless been followed by its distention with flatus. Or they might call attention to the tympanites of typhus fever, and other kindred disorders, in which little food has been taken for a long period of time. But a little reflection might teach us that none of these instances have absolutely excluded the presence of all alimentary substances ; and that a very small quantity of liquid or solid matter would probably be quite sufficient to yield the gases observed.
4. Lastly, as regards the intestinal gases present in diseased subjects, we may conjec ture a fourth source of such elastic fluids :— namely, the decomposition of the various secretions of the canal. For it is not too much to assume, that the decomposition to which the alimentary contents of the intestine appear to be often exposed, is sometimes shared by the secretions poured into its* cavity ; especially when we recollect that, in many dis eases, the state of all the fluids of the organism is frequently such as notoriously favours the access of putrefaction in the tissues after death.
The gases expelled from the large intestine carry with them the odorous principles of the excrement. It is, indeed, probable that they become impregnated with these volatile sub stances mechanically, as a necessary result of their contact with them in the bowels. But reasons are not wanting for the conjecture, that the introduction of certain fcetid substances into the blood, is subsequently followed by their specific determination to the mucous membrane of the intestinal canal ; which thus forms a channel for their elimination from the system. For after the inhalation of any par ticularly offensive odour, the fmces and flatus often exhibit what is unmistakeably the same smell, in a very concentrated form. And the active diarrhcea which frequently attends this reproduction of the odour, seems a part of the same effort of nature, towards the removal of what other evidence, beside that of our senses, thus testifies to be an active poison.