the albumin, but is a second stage in the process of hydration. The albumoses formed directly from albumin (i.e. proto- and hetero-albumose) are called primary albumoses. Deutero-albumose is thus nearest to the peptones, not only in its reactions, but also in its method of formation.

If the three primary cleavage products of digestion be separated and subjected to further digestion, peptone is the ultimate result in each case. Proto-albumose yields hemi-peptone'; the deutero-albumose, which is an intermediate stage in the process, is termed hemi-deuteroalbumose, as it yields hemi-peptone. Hetero-albumose indicating its double origin yields both anti- and hemi-, that is, ampho-peptone, the intermediate deutero-albumose being correspondingly named amphodeutero-albumose. The anti-albuminate is first changed into the insoluble anti-albumid, which slowly yields anti-peptone, with an intermediate stage of anti-deutero-albumose.

Digestion in the stomach never goes further than the formation of peptone; leucine and tyrosine are not formed. Such is, so far as is at present known, the series of changes which albumin undergoes.

Fibrin is first dissolved, forming a solution of globulins (see p. 233), and these are then converted into the same series of products with peptone as the terminal product. The products of globulin may be termed globuloses; of vitellin, vitelloses; of casein, caseoses; of myosin, myosinoses; and these are very like the albumoses; any slight variations that may occur have been already alluded to in the descriptions already given of the separate proteids. They may be all conveniently grouped together under the general term proteoses. The products of digestion of elastin (p. 475) and of gelatin (p. 472) have a general resemblance to the proteoses and peptones. Mucin, keratin, and nuclein are not digested in the stomach. Hæmoglobin is split into hæmatin and acid-albumin; the former remains unchanged, the latter is digested. Except that the proteid envelopes of fat-cells are dissolved, fats are not altered in the stomach. Starch is also unaltered. Cane sugar is said to be partially converted into dextrose and lævulose by the mucin of the stomach.3

We thus see that the stomach acts for all practical purposes on only one of the proximate principles of food, namely, the proteids. Why the stomach does not digest itself during life is a question that

1 Proto-albumose has never yet been obtained absolutely free from hetero-albumose; the purer it is, the less anti-product does it yield; Neumeister therefore concludes that if it were entirely free from impurity it would yield a pure hemi-peptone.

2 Except in the stomachs of such animals as the horse and pig, where an alkaline juice is secreted for the first hour or so after the arrival of food (see pp. 612, 628). 3 This action is, however, very slight (Komanos, Diss. Strasburg, 1875).

1

has never yet received an answer. John Hunter's view that it is due to a 'living principle' is no real explanation. The stomach after death may at a suitable temperature digest itself, and self-digestion may also occur in ulcerated portions of the stomach-wall where the circulation has been stopped, and so lead to perforation. But the mere alkalinity of the blood and lymph bathing the stomach is not the whole secret of its power of resisting the action of the acid juice; for the intestines and the pancreas are similarly able to withstand the digestive action of the pancreatic juice, which is most energetic in alkaline media.

Pathological and other abnormal conditions of gastric digestion.-We have seen the conditions under which gastric digestion is most favourably carried on; we have now to see those which hinder or interfere with, or accompany, disorders of digestion in the stomach.

All salts of the heavy metals, such as mercuric chloride or lead acetate, which form precipitates with pepsin and proteids, completely stop both artificial and natural digestion. Concentrated solutions of alkaline salts (sodium or magnesium sulphate, &c.), which produce transudation of fluid into the stomach, act similarly; and quite small percentages of such salts (such as 0·004 per cent. of sulphate of sodium, potassium, ammonium, or magnesium, 0·02 of various urates, 0·01 of sodium phosphate, &c.) have a very considerable inhibitory effect when acid solutions of pure pepsin are used in experiments on artificial digestion; the same is true for trypsin (Nasse,2 Heidenhain,3 A. Schmidt, E. Stadelmann "). Phenol must be somewhat concentrated to stop gastric digestion. Bitters, according to Buchheim, do not further gastric digestion; but common experience is against this; like pepper they stimulate the mucous membrane to secrete.

4

6

An admixture with the gastric juice which is not uncommon in pathological states is bile. If this enters the stomach from the intestine, it precipitates the proteids, and prevents them entering that swollen condition so essential for gastric digestion. It also neutralises the gastric juice and thus entirely stops the activity of pepsin. Should, however, the pancreatic juice enter with the bile, it may happen that pancreatic digestion occurs in the stomach.7

To speak of all the varied pathological conditions of the stomach would be beyond the scope of this work. Our knowledge is in many cases the result of inference from the good or bad effects of certain

1 Phil. Trans. 1772.

4 Ibid. xiii.

2 Pflüger's Archiv, xi.

5 Zeit. Biol. xxv. 208.

6 Buchheim, Beiträge z. Arzneimittellehre, Leipzig, 1849, Heft i.

7 Hoppe-Seyler, Physiol. Chem. p. 233.

p. 112.

3 Ibid. x.

methods of treatment; except in those cases where there is vomiting or a fistula, we can but rarely examine the actual stomach contents.

The two chief forms of dyspepsia are (1) the atonic, where there is, as Beaumont observed, a condition of the stomach much resembling the furred tongue of the patient. The secretion is scanty; this is often owing to anæmia, and an imperfect blood-supply may lead to ulceration of the stomach-walls; fever also, as Beaumont showed, produces much the same effect; even mechanical stimulation of the stomach calls forth little or no secretion. (2) Irritative dyspepsia; in this the stomach is in a state of active congestion; the blood-supply is greater than normal; an excess of fluid is poured out into the stomach; but in these catarrhal conditions the fluid is not gastric juice, but an alkaline transudation.1

In special diseases of the alimentary canal the digestive juices, it need hardly be said, are abnormal. Thus in typhoid fever there is little or no pepsin secreted (Hoppe-Seyler 2); in cancer some observers have stated there is no hydrochloric acid formed3; others have found the acid; probably the cases vary a good deal in this particular.4

Putrefaction does not occur normally in the stomach; bacteria do not flourish in an acid medium; but in various conditions in which the normal acid is absent, or masked by excess of alkaline transudation, fermentations set up by bacteria, sarcina, and other fungi may

occur.

In

Thus in certain cases alcoholic fermentation may take place; more frequently the lactic and butyric fermentations are set up. these and other changes of a similar kind certain of the products are gaseous (carbonic acid, hydrogen, marsh gas) and distend the stomach, passing off ultimately in eructations. The gases are in these cases mixed with air, of which a small quantity is always swallowed with the food. On the next page are some analyses of gases from the stomach; the numbers are percentages of volume.

Gastric juice in invertebrates.—The only research I have been able to find in connection with this subject is that of Stamati 5 on the gastric juice of the crayfish. This was obtained by means of a fistula, and was found to be yellowish and alkaline; it forms peptones from proteids, sugar from starch, and emulsifies fats, liberating fatty acids. Its action thus resembles that of the pancreatic juice of vertebrates.

1 A most important paper on this subject is one by Leube, Deutsch. Arch. f. klin. Med. xxxiii.

2 Physiol. Chem. p. 242.

3 v. d. Velden; Kredel, Zeit. f. klin. Med. vii. 592; Riegel, Deutsch. Arch. f. klin. Med. xxxvi. 100.

4 H. Köster, Maly's Jahresb. xv. 287; see also Maly, Maly's Jahresb. xiv. 290, footnote. 5 Compt. rend. soc. biol. (2) v. 16.

1 Plauer, Sitzungsb. Wien. Akad. xlii.

2 Ewald and Rupstein, Arch. f. Anat. u. Physiol. 1874, p. 217.

CHAPTER XXXI

DIGESTION IN THE INTESTINES

THE greyish, acid, pap-like material that leaves the stomach by the pyloric orifice is called chyme; it enters the small intestine, and is slowly propelled along it, and subsequently through the large intestine, by the peristalsis of the muscular coats. The chyme excites the pouring out of the secretions from the pancreas, the liver, and the intestinal glands. These juices are all alkaline; the acidity of the chyme is neutralised and the activity of the pepsin which left the stomach is brought to an end. When the bile meets the chyme the turbidity of the latter is increased, owing to the precipitation of certain proteids ; an alkaline juice like the bile would naturally precipitate any acidalbumin, but this is not its only action. The bile-salts form with the undigested albumin, and also with the albumoses (not with true peptone), a precipitate independent of the reaction. It has been surmised that this conversion of chyme into a resinous, viscid mass is to hinder somewhat its progress through the intestine; it clings to the intestinal wall, thus allowing absorption to take place.

The intestinal contents become alkaline about ten or twelve inches from the pylorus, and then pancreatic digestion begins. This secretion continues the work commenced in the mouth and stomach, and also acts on fats; the succus entericus and bile are of minor importance. Putrefactive organisms abound and produce substances to be described later. The reaction of the intestinal contents remains alkaline until the large intestine is reached; fermentative processes have by this time produced sufficient lactic, butyric, and similar acids to more than neutralise the alkalinity of the juices. This acidity stops the digestive action of the pancreatic juice.

As the contents pass along the intestine, soluble matters are produced and then absorbed, and thus the amount of chyme is gradually diminishing. In such animals as the dog, where digestion is active and the nature of the food almost entirely digestible, the intestine will be almost empty six to nine hours after a full meal. The amount of undigested residue, which ultimately forms the fæces, is much larger in those animals, like herbivora, whose food contains a quantity of indigestible material like cellulose.