That element of the fxces which is derived from the digestive organs of the animal itself, consists chiefly of mucus and precipitated bile. This mucus is, for the most part, structure less ; but is mixed with variable quantities of scaly epithelium from the rectum in the neigh bourhood of the anus. In violent diarrhcea, columnar cells from the intestine may also be found in the evacuations :—sometimes in the younger cell-form of abortive cytoblasts or nuclei, sometimes in the more advanced state of simple ovoid cells. The latter are sometimes met with in small numbers, even in healthy fxces ; and constitute what are often termed mucus-corpuscles. The biliary constituent is found chiefly in the form of minute amorphous masses or molecules of a resinous character; crystals or plates of cholestearine ; and soluble colouring matter, that often stains the cells just mentioned, as well as the other mechanical constituents of the excrement.
The crystals of ammoniaco-phosphate of magnesia, Nthich are so often found in the fmces, can hardly be definitely allotted to either of the two foregoing sources. They are easily recognised by their characteristic shape. They were formerly supposed to be peculiar to the stools of diarrhcea and typhus. But they are found in the healthiest fces. Their occurrence appears to be favoured by all circumstances which further decomposi tion. They are therefore probably due to the action of ammonia (developed in the fmces before or after their expulsion) upon that neutral phosphate of magnesia, which we shall see forms so large a proportion of the entire saline constituent of the excrement.
The chemical composition of the fmces will of course exactly correspond with the nature and amount of those substances of which it forms the mechanical admixture. Hence, not only is it impossible to lay down any average that can apply to fces generally, but it is even probable, that no two specimens of excre ment are composed of the sanae proximate constituents mingled in the same proportions.
Berzelius* analyzed the ficces of a labourer who had fed on coarse, hard-baked bread, with moderate quantities of meat and vegetables.
He obtained the following results :— _ _ Without, however, impugning the accuracy of an analysis conducted by such an eminent chemist as Berzelius, it seems important to point out that, for physiological purposes, it is all but useless. For not only does it afford no inference as to the quantitative composition of the fxces generally, but it even suggests grave doubts as to the correctness with which its own chief results have been grouped toge ther. Recalling, for example, our subdivision
of the constituents of the fxces into alimen tary and secretory, we inquire in vain how much of the soluble albumen and extractive of this analysis was derived from the food, and how much may be ascribed to the secre tions poured into the canal. In like manner we are ignorant whether its fatty constituent was not partly the undigested residue of fat which had been introduced with the food. But from a comparison of this analysis with some observations on the meconium by Hoefle* and Lehmann we may conjecture, that while the protein compounds found in healthy ex crement belong almost exclusively to the food, a small quantity of its elain and margain, and a larger amount of its muco-gelatinous ex tractive, are derived from the secretions of the animal itself.
The inorganic constituents of the excre ment must also vary greatly with the nature and amount of its alimentary residuum. Portert states that healthy fxces, when dried, contain on an average about 6.7 parts per cent. of mineral substances. Wehsarg reckons these salts at 4.1 per cent., from an average of seven analyses. But an analysis by Dr. Percy§ estimates thein at 16.4 per cent. This proportion somewhat approaches that given in the analysis by Berzelius quoted above. It also corresponds with some ana lyses by Macaire and Marcet II of the fces of the Dog and Horse, which they fouild to contain 20 and 23 per cent. of ash respec tively.1 The soluble salts form between one fourth and one-third of the whole ash. The phosphates of the earths and alkalies consti tute about one-third of all the salts present. While the chlorides of the alkalies are reduced to the very small proportion of about one thirtieth ; a proportion which is about equalled by the whole of the sulphates. The chief re maining peculiarities worthy of notice are, that the quantity of potash is from 10 to 40 times greater than that of the soda; and that the magnesia reaches half the amount of the lime. Of these two quantitative disproportions, the first seems due to the food; while the latter has been referred by Berzelius to the more active absorption of lime than magnesia in the intes tinal canal. Carbonates of the alkalies are found in the ash of human excrement ; but they are apparently almost absent from that of the Sheep, Cow, and Horse. They are pro bably produced by a combustion of some or ganic salts of these bases.