HISTORICAL ACCOUNT OF DIGESTION. 289 



the intestinal mucous membrane, but in some fishes, e.g., the shark, there is a spiral valve. [The 

 inversive (cane-sugar) ferment is wanting in the herbivora, as the cow, horse, and sheep, but is 

 present in the dog and cat. It is also met with in birds and reptiles, and in many of the 

 invertebrates, as the ordinary earth-worm (M. Hay).] 



In amphibia and reptiles the stomach is a simple dilatation ; the gut is larger in vegetable 

 feeders than in flesh feeders. The liver is never absent in vertebrates, although the gall-bladder 

 frequently is. The pancreas is absent in some fishes. 



Digestion in Plants. The observations on the albumin-digesting power of some plants 

 are extremely interesting (Canby, 1869 ; Ch. Darwin, 1875). The sundew or drosera has a 

 series of tentacles on the surface of its leaves, and the tentacles are provided with glands. When 

 an insect alights upon a leaf, it is suddenly seized by the tentacles ; the glands pour out an acid 

 juice over the prey, which is gradually digested, all except the chitinous structures. The secre- 

 tion, as well as the subsequent absorption of the products of digestion, are accomplished by the 

 activity of the protoplasm of the cells of the leaves. The digestive juice contains a pepsin-like 

 ferment and formic acid. Similar phenomena are manifested by the Venus flytrap (Dionaea), 

 by pinguicula, as well as by the cavity of the altered leaves of nepenthes. About fifteen species 

 of these ' ' insectivorous " or carnivorous plants are known. [Papain, and other ferments analo- 

 gous in their action to trypsin, are referred to in 170.] 



188. HISTOEICAL. Digestion in the Mouth. The older observers regarded the saliva as a 

 solvent, and in addition, many bad qualities, especially in starving animals, were ascribed to it. 

 This arose from the knowledge of the saliva of mad animals, and the parotid saliva of poisonous 

 snakes. The salivary glands have been known for a long time. Galen (131-203 a.d.) was ac- 

 quainted with Wharton's duct, and Aetius (270 a.d.) with the sub -maxillary and sub-lingual 

 glands. Hapel de la Chenaye (1780) obtained large quantities of saliva from a horse, in which 

 he was the first to make a salivary fistula. Spallanzani (1786) asserted that food mixed with saliva 

 was more easily digested than food moistened with water. Hamberger and Siebold investigated 

 the reaction, consistence, and specific gravity of saliva, and found in it mucus, albumin, common 

 salt, calcium and sodium phosphates. Berzelius gave the name ptyalin to the characteristic 

 organic constituent of saliva, but Leuchs (1831) was the first to detect its diastatic action. 



Gastric Digestion. Digestion was formerly compared to "coction," whereby solution was 

 effected. According to Galen, only substances that have been dissolved passed through the 

 pylorus into the intestine. He described the movements of the stomach and the peristalsis of the 

 intestines. Aelian gave names to the four stomachs of the ruminants. Yidius (t 1567) noticed 

 the numerous small apertures of the gastric glands. Van Helmont (t 1644) expressly notices 

 the acidity of the stomach. Reaumur (1752) knew that a juice was secreted by the stomach, 

 which effected solution, and with which he and Spallanzani performed experiments on digestion 

 outside the body. Carminati (1785) found that the stomachs of carnivora during digestion 

 secreted a very acid juice. Prout (1824) discovered the hydrochloric acid of the gastric-juice, 

 Sprott and Boyd (1836) the glands of the gastric mucous membrane, while Wasmann and Bischoff 

 noted the two kinds of gastric-glands. After Beaumont (1834) had made his observations upon 

 Alexis St Martin, who had a gastric fistula caused by a gunshot wound, Bassow (1842) and 

 Blondlot (1843) made the first artificial gastric-fistulse upon animals. Eberle (1834) prepared 

 artificial gastric-juice. Mialhe called albumin, when altered by gastric digestion, albuminose ; 

 Lehmann, who investigated this substance more carefully, gave it the name peptone. Schwann 

 isolated pepsin (1836), and established the fact of its activity in the presence of hydrochloric acid. 



Pancreas, Bile, Intestinal Digestion. The pancreas was known to the Hippocratic School; 

 Maur. Hoffmann (1642) demonstrated its duct (fowl), and Wirsung described it in man. Regner 

 de Graaf (1664) collected the pancreatic juice from a fistula, and Tiedemann and Gmelin found 

 it to be alkaline, while Lauret and Lassaigne found that it resembled saliva. Valentin dis- 

 covered its diastatic action, Eberle its emulsionising power, and CI. Bernard (1846) its tryptic 

 and fat-splitting properties. The last-mentioned function was referred to by Purkinje and 

 Pappenheim (1836). Aristotle characterised the bile as a useless secretion; according to 

 Erasistratus (304 B.C.), fine invisible channels conduct the bile from the liver into the gall- 

 bladder. Aretaeus ascribed icterus to obstruction of the bile-duct. Benedetti (1493) described 

 gall-stones. According to Jasolinus (1573), the gall-bladder is emptied by its own contractions. 

 Sylvius noticed the lymphatics of the liver (1640); Walaeus, the connective-tissue of the so- 

 called capsule of Glisson (1641). Haller indicated the uses of bile in the digestion of fats. The 

 liver-cells were described by Henle, Purkinje, and Dutroch'et (1838). Heynsius discovered the 

 urea and CI. Bernard (1853) the sugar in the liver, and he and Hensen (1857) found glycogen 

 in the liver. Kiernan gave a more exact description of the hepatic blood-vessels (1834). Beale 

 injected the lymphatics, and Gerlach the finest bile-ducts. Schwann (1844) made the first 

 biliary fistula ; Demarcay particularly referred to the combination of the bile-acids with soda 

 (1838) ; Strecker discovered the soda compounds of both acids, and isolated them. Celsus 

 mentions nutrient enemata (3-5 A.D.). Fallopius (1561) described the valvulse conniventes and 

 villi of the intestinal mucous membrane, and the nervous plexus of the mesentery. The 

 agminated glands or patches of Peyer were known to Severinus (1645). 



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