5 In speaking of the properties of the bile, I may mention that, although bile has no digestive power (properly speaking) over albuminous substances, yet, when injected into the subcutaneous cellular tissue of a healthy animal, it eats its way out through the skin, just as gastric juice or lactic acid does under similar circumstances. Even the muscles with which it comes in contact appear to be eaten away.
6 Vide a Discourse on the Chemistry of Digestion, by Dr. Marcet. Journ. of the Chem. Soc., Oct. 1862.
7 "Die Verdauungssaefte und der Stoffwechsel." Leipzig, 1852.
Further, these last-named observers found that, while the chyle in the thoracic duct of a healthy dog contains 32 parts of fat per thousand, that in the thoracic duct of a dog with a ligatured gall-duct, contains only 2 parts per thousand. These facts clearly prove that bile plays an important part in the absorption of the fatty portion of our food. Next comes the question, "In what manner does bile aid in the absorption of fatty matter?" As is well known, fats or oils have no tendency to mix with water, and hence diosmose between an aqueous and an oily fluid is next to impossible. Matteucci has, however, shown that if an animal membrane be moistened on both sides with a weak solution of potash, it allows oil to pass through it. It has also been observed, that when the intestine is moistened with bile, it allows oil to pass through, which would not otherwise be the case. To illustrate this property of bile, I performed the following experiments:—
Firstly,—A clean piece of duodenum was filled with oil, ligatured at both ends, and suspended in water, holding in solution a small quantity of albumen. (The albumen was added to the water merely to imitate slightly the albuminous blood.) On examination, twenty-four hours later, no oil was found to have escaped through the intestinal walls.
Secondly,—A second portion of intestine had its internal surface moistened with sheep's bile before the introduction of the oil. It was then treated in the same manner as the preceding, and on being examined after the lapse of twenty-four hours, a small quantity of the oil was found to have penetrated through the intestine.
Thirdly,—Into a third portion of intestine was poured equal parts of sheep's bile, and chyme obtained from a dog in full digestion, through a fistulous opening into its stomach. After being treated for the same length of time, and in precisely the same manner as the others, evident signs of the oily matters of the chyme having passed through the walls of the intestine were obtained, for they were seen as a scum floating on the surface of the albuminous water. Moreover, the fatty matters were not in the form of pure oil, but of a soapy substance.
The bile is thus seen to possess one of the more remarkable properties of the pancreatic juice. There is this important difference between the action of these two secretions on fats, however, that while bile merely emulsions and saponifies that portion of our food which enters the duodenum in the form of fatty acids, pancreatic juice, on the other hand, possesses the power, not only of emulsioning and saponifying the fatty acids, but also the neutral fats; indeed, its power seems chiefly to be exerted upon the latter. Hence it appears that both secretions are in a measure necessary to the complete digestion and absorption of the oleaginous constituents of our food.
On one occasion, while experimenting with bile at University College, I was surprised to hear Minton, the servant who was assisting me, say, that while he was travelling with Sir Andrew Smith in South Africa, he had oftentimes seen the Caffres drink bile direct from the gall-bladders of the animals killed by the European party, and that, while passing the gall-bladder round to each other, they would rub their stomachs and say,—"Mooé-ka-kolla," signifying thereby, that it was very good. It certainly seems very extraordinary that any human being should not only drink, but drink with pleasure, a liquid so bitter and nauseating as bile. Perhaps the poor Caffres, however, drank the sickening tasted bile for the same reasons as the cattle in Caffreland, at certain periods of the year, go thousands of miles to drink at the salt-springs. There being scarcely any chloride of sodium in the earth, there is insufficient for the animal requirements in the herbage on which they feed, and they are forced to supply the deficiency by artificial means. Bile contains a large percentage of soda, and perhaps the Caffres drink it in order to obtain that substance, just as the animals drink the brackish water of the salt licks, feeling that it agrees with them, without knowing why.
THE MECHANISM OF JAUNDICE.