384 HISTORICAL ACCOUNT OF DIGESTION. 



stomach consists of a glandular proventriculus and a strong muscular stomach 

 which is covered with horny epithelium and triturates the food. There are 

 usually two fluid diverticula on the small intestine near where it joins the large 

 gut. In Fishes the intestinal canal is usually simple ; the stomach is merely a 

 dilatation of the tube ; and at the pylorus there may be one, but usually many, 

 blind glandular appendages (the appendices pyloricse). There are usually longi- 

 tudinal folds in the intestinal mucous membrane, but in some fishes, e.g. t the shark, 

 there is a spiral valve. [It is curious to find that the inversive (cane-sugar) fer- 

 ment is wanting in the herbivora, as the cow, horse, and sheep, but is present in 

 the carnivora, as the dog and cat. It is also met with in birds and reptiles, and 

 in many of the invertebrates, as the ordinary earth-worm (Matthew 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 (Canby, 1869; Ch. Darwin, 1875) are extremely interesting. The 

 sundew or drosera has a series of tentacles on the surface of its leaves, and the 

 tentacles are provided with glands. As soon as 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 secretion, 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 con- 

 tains a pepsin-like ferment and formic acid. Similar phenomena are manifested 

 by the Venus flytrap (Dionsea), 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. 



188. Historical. 



Digestion in the Mouth. The Hippocratic school was acquainted with the 

 vessels of the teeth ; Aristotle ascribed an uninterrupted growth to these organs, and 

 he farther noticed that animals that were provided with horns, and had cloven 

 hoofs, had an imperfect set of teeth the upper incisors were absent. It is curious 

 to note that in some cases where men have had an excessive formation of hairy 

 appendages, the incisor teeth have been found to be badly developed. The muscles 

 of mastication were known at an early period ; Vidius (t!567) described the tempero- 

 maxillary articulation with its meniscus. 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. Human saliva, without organisms, is 

 poisonous to birds (Gautier). The salivary glands have been known for a long 

 time. Galen (131-203 A.D.) was acquainted with Wharton's duct, and Ae'tius 

 (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 (1S31) was the first to detect its diastatic action. 



Gastric Digestion. Digestion was formerly compared to boiling, whereby 

 solution was effected. According to Galen, only, substances that have been dis- 

 solved passed through the pylorus into the intestine. He described the move- 

 ments of the stomach and the peristalsis of the intestines. Aelian gave names to 



