Oxygen and sulphuretted hydrogen were found in traces only; Hofmann found no marsh gas in rabbits. The carbonic acid, as is seen in the above tables, is always present in large quantities, especially in the large intestine, and especially when the diet is vegetable. Its sources are the decomposition of carbonates, acetates, and lactates in the food, the alcoholic fermentation of dextrose in the intestine, the putrefaction of carbohydrates (especially cellulose) and proteids, the butyric fermentation of lactic acid, and the putrefaction of choline. The enormous quantity of gas discharged in cases of hysterical flatulence consists largely of carbonic acid; it is possible it may have simply diffused from the blood-vessels. The hydrogen is most abundant on a milk diet; its source is the butyric acid fermentation of lactic acid (p. 103). The marsh gas is derived from the decomposition of acetates and lactates. Hoppe-Seyler1 represents the decomposition of calcium acetate by the equation (C2H ̧O2)¿Ca+H2O=CaCO3+CO2+2CH. It is also derived from the decomposition of cellulose (Hoppe-Seyler,2 Tappeiner,3 Henneberg and Stohmann'). Hoppe-Seyler's formula for the reaction is CH10O5+ H2O=3CO2+3CH. Henneberg and Stohmann consider that hydrogen, acetic acid, and butyric acid are also formed, their equation for the reaction being 21C6H10O5+11H,O=26CO2+10CH, +6H2+19C2H ̧О2+13C ̧H ̧О2; whichever equation is correct, the fact remains unaltered that a vegetable diet is that which yields most marsh gas. A third and small source of marsh gas is from the choline of lecithin (Hasebroek 5). The nitrogen is derived chiefly from the swallowed air; the oxygen is largely absorbed; nitrogen is also contained in the ammonia, which is the result both of pancreatic digestion and putrefaction of proteids. The hydrogen sulphide is derived wholly from the putrefaction of proteids. We may in conclusion briefly glance at the matter of putrefaction from another point of view, namely, its action on each class of the proximate principles of food. Action on futs.---This is a fat-splitting action, exactly similar to that produced by the steapsin of the pancreatic juice. Putrefaction in addition produces lower acids (valerianic, butyric, &c.) of the fatty series. Lecithin is similarly decomposed into its acid (glycero-phosphoric) and choline which then breaks up into carbonic acid, marsh gas, and ammonia. Action on carbohydrates.-The chief fermentation here is the lactic acid followed by the butyric acid fermentation (see p. 103). 1 Zeit. physiol. Chem. ii. 561. 3 Zeit. Biol. xx. 52; xxiv. 105. 4 Ibid. xxi. 613. 2 Ibid. x. 201, 401. With regard to cellulose it may be here stated that putrefaction is the only known change that this constituent of food undergoes in the alimentary canal. Henneberg and Stohmann nevertheless consider it a source of energy. An important practical point in cattle feeding, whether cellulose economises the decomposition of proteid, has not yet passed beyond the regions of dispute (v. Knierem,2 Weiske, and others 3). Action on proteids. The antipeptone is decomposed with more difficulty than the hemipeptone. The products of putrefaction of proteids are ammonia, sulphuretted hydrogen, ammonium sulphide, volatile and fatty acids; amines and amido-acids, especially leucine and tyrosine; indole, skatole, phenol, and cresol, phenyl-propionic, and phenyl-acetic acids, and the aromatic oxy-acids, hydroparacumaric and parahydroxyphenylacetic acids. The presence of these numerous acid compounds, especially of lactic acid, gives the contents of the large intestine, as a rule, an acid reaction. The presence of indole and skatole gives the faces their characteristic odour; they are, however, very largely absorbed and excreted as ethereal sulphates in the urine. With regard to the production of indole, Harris and Tooth' found that its appearance, and that of its allies, is capricious, and can be easily prevented in artificial pancreatic digestion. The smallest amount of mercuric chloride or phenol, even if not sufficient to render the fluid aseptic, prevents the formation of these substances. Whenever indole is present, however, large numbers of all sorts of bacteria are present also; still it may be absent even if swarms of microorganisms are present. It thus appears that there are special indole-forming organisms. As a result of inoculation experiments, it was found that indole was formed from peptone, not from leucine and tyrosine. It is interesting to note that certain products of putrefaction, especially phenol or carbolic acid, and cresol are antiseptics; the microbes thus produce compounds which, if allowed to accumulate, would ultimately destroy their life. It is considered by certain observers that the production of poisonous alkaloids is a normal process in the alimentary canal, that these are absorbed, and if excessive in amount may produce self-poisoning or 'auto-intoxication.' As a rule, they are excreted, however, by the kidney, and thus the body generally escapes their poisonous action (Bouchard). Such a doctrine must be considered unproven for the present. The most careful of the numerous researches in this direction entirely negative the idea. Ptomaines are absent, not only in normal urine and fæces, but also in these excretions in various diseases. There is, however, some evidence of their formation in typhoid fever, cholera, and cystinuria. We have seen that under normal circumstances choline, a typical instance of a poisonous animal alkaloid, is broken up into simple non-poisonous products by the intestinal bacteria; and it is exceedingly probable that if other alkaloids are produced by bacteria in the intestine, they also are promptly destroyed by other species of the same micro-organisms (see also Chapter XIII). 1 Bunge surmises (Physiol. Chem. 192) that the epithelium cells of the intestine may have a similar action on cellulose. He also dwells (p. 81) on the important action of cellulose as a mechanical stimulus to peristalsis. 2 Zeit. Biol. xxiv. 293. 3 Ibid. xxii. 373. 4 Journ. of Physiol. ix. 220. CHAPTER XXXVI THE FECES THE fæces consist of the indigestible and undigested portions of the food, products formed from food-stuffs by the digestive ferments (indole, skatole, soaps, &c.), and certain constituents of the digestive secretions (mucin, altered bile-pigment, &c.). The amount of the fæces varies with the amount and character of the food. Over-eating entails voluminous excrements, since, though much of the food taken may be digestible, it escapes digestion and absorption simply because its amount is too great for the digestive ferments to act upon, or for the absorbing surface to come in contact with. On a mixed diet of moderate amount in man, Liebig calculated that the weight of the fæces is one-seventh to one-eighth of the food taken. Calculating both food and fæces in the dry state, Bischoff and Voit found in dogs that with a nitrogenous diet the fæces weighed onetenth to one-fourteenth, with a bread diet one-sixth to one-eighth of the food. The amount of water in the fæces varies considerably in health from 68 to 82 per cent. In diarrhoea it is more abundant still. The constituents of the fæces may be classified as follows: 1. Undigested foods: fats, carbohydrates, and proteids, if any of these are present in excess in the food. On a moderate diet, unaltered proteid is never found. 2. Indigestible constituents of the food: cellulose, keratin, mucin,' chlorophyll, gums, resins, cholesterin. 3. Constituents digestible with difficulty: uncooked starch, tendons, elastin, nuclein, various phosphates, and other salts of the alkaline earths. 4. Products of decomposition of the food : indole, skatole, phenol, &c.; fatty acids, formic, acetic, butyric, isobutyric,2 caproic, valerianic; other acids, lactic, malic, succinic, &c. Some of these acids are free; some in combination with ammonia and other bases; hæmatin from hæmoglobin; 3 soaps, especially calcium and magnesium soaps of oleic, palmitic, and stearic acids (the soluble soaps are, of course, to a large extent 1 Mucin which has been separated out by means of lime water and acetic acid is readily digestible by artificial pancreatic juice (see p. 481). Mucin as contained in mucus, however, appears to be quite unaltered by the natural juices. 2 Brieger, Ber. deutsch. chem. Ges. x. 1027. 3 Hoppe-Seyler, Physiol. Chem. p. 339. absorbed); stercorin, a product of decomposition of cholesterin; this substance was described by Flint,' but its existence is very doubtful ; excretin (C20H3,0), another doubtful substance described by Marcet.2 36 5. Bacteria of all sorts and debris from the intestinal wall: cells, nuclei, mucus, &c. L. Hermann 3 found in a loop of intestine separated in the manner of Thiry and Vella that at the end of some weeks it was filled with bacteria, cellular débris, and often fat, the whole mass having a fæcal appearance. 6. Bile residues: these are mucin, traces of bile-acids and their products of decomposition; cholesterin and lecithin, the latter in traces. only are also found; these two substances also partly owe their origin to the ingested foods. The bile-pigments as such are not present, but are changed into a substance like hydro-bilirubin, which is called stercobilin. Stercobilin may originate also from the hæmatin in the food (MacMunn). Hoppe-Seyler, however, who made experiments on dogs, found that hæmatin is easily discoverable in the fæces, and regards it as improbable that stercobilin originates from the hæmoglobin of the food. This subject merits renewed study, and the experiments should be made on animals in which no bile is allowed to enter the intestine. The meat of the food cannot, however, be a large contributor to the pigments of the faces, as the stools of jaundiced persons are claycoloured even if they are on a meat diet. Hydro-bilirubin and stercobilin are usually considered to be produced by reduction processes : MacMunn, however, regards the formation of stercobilin as one of intermediate oxidation; by further oxidation it may be transformed into a substance like choletelin, the most highly oxygenised product of the bilepigment with which we are acquainted. T. J. Walker has recorded two cases in which the liver was apparently healthy, but the pancreatic duct was occluded; the fæces in these cases were free from stercobilin, being clay-coloured as in jaundiced persons. He therefore concludes that the pancreatic ferment is in some way necessary for the formation of the fæcal pigment. Stereobilin may be most readily prepared by extracting the fæces with acidulated alcohol (17 parts of rectified spirit to 3 of sulphuric acid); the extract is diluted with water, and shaken with chloroform ; the chloroform dissolves out the pigment and may be driven off by evaporation. Recherches exp, sur une nouvelle fonction du foie, Paris, 1868. 2 Ann. de chem. et de phys. lix. 91. 3 Du Bois Reymond's Archiv, 1889. 4 Vaulair and Masius, Centr. med. Wiss. 1871, No. 24. 5 Journ. of Physiol. x. 115. 6 Physiol. Chem. p. 339. 7 Medico-Chirurgical Trans. vol. lxxii. 1889, p. 257. Before proceeding to describe the spectroscopic appearances of this substance it must be acknowledged that as yet spectroscopic analysis is the only method yet applied to this and related pigments (hydro-bilirubin, urobilin, &c.); it is possible in the future that other methods of investigation may confirm or correct the knowledge obtained by the spectroscope. Another possible source of error is the admixture of unchanged hæmatin with such pigments, and a third difficulty arises from the fact that there are probably intermediate products between bilirubin and stercobilin which occur in different proportions in different preparations. This last assumption is confirmed by the differences obtained in measurements of the bands of stercobilin in different preparations. One of these intermediate products appears to be absorbed, carried to the liver, and there excreted into the bile as biliary urobilin (p. 685); by further oxidation biliary urobilin can be artificially changed into a pigment closely resembling stercobilin. The absorption spectrum of stercobilin is practically identical with that of hydro-bilirubin (fig. 88, spectrum 3, p. 685). We have seen, however, that hydrobilirubin after treatment with zinc chloride and ammonia shows a green fluorescence and a three-banded spectrum; stercobilin, on the contrary, though it shows the same fluorescence, gives a four-banded spectrum. There are also certain differences in the spectra of the two substances aftertreatment with other reagents, such as soda, or zinc chloride by itself, or ammonia by itself. The spectroscope thus teaches us that the two substances cannot be identical. Still more does the spectroscope teach us the non-identity of either of these pigments with urobilin. Jaffé and Maly first described urobilin, and considered that it originated from bilirubin, that bilirubin was changed into hydro-bilirubin in the intestine, and then partly absorbed and excreted in the urine. Subsequent investigations have, however, shown that there are two pigments or their chromogens in the urine which have each received the name urobilin; one is normal urobilin, which shows the same spectrum as choletelin, that is one band only (at F); the other pathological urobilin which occurs in certain diseased conditions is possibly identical with stercobilin, and no doubt originates in the intestine as Maly considered. Normal urobilin does not necessarily arise in the intestine from stercobilin; in Copeman and Winston's case of biliary fistula, no bile entered the intestine, but the urine was not colourless; it contained ordinary urobilin. In cases of extravasation of blood, the destruction of blood-pigment may give rise to pathological urobilin in the urine, and moreover normal urobilin was obtained artificially by Mac Munn by acting on acid hæmatin with hydrogen peroxide. Pathological urobilin is regarded by MacMunn as a less highly oxidised product than normal urobilin. It thus appears that if the urine pigment be formed in the liver, it is unnecessary for it to go through the stage of bile-pigment, though this stage probably occurs under normal circumstances. This subject will be more fully dealt with under Urine (Chapter XLI). Meconium The meconium, or the contents of the intestine of new-born children, is a greenish-brown, almost black, viscid material. Its reaction is generally acid. On microscopic examination it shows leucocytes, often stained green, columnar epithelium cells from the 1 Centralbl. med. Wiss. 1863, p. 241. 5 Journ. Physiol. x. 213. 2 Ann. Chem. Pharm, clxi. 368; clxiii. 77. 4 Cases recorded by MacMunn, Ibid. p. 83. |