172 



DIGESTION 



FIG. 7', 



Thus, the Venus' flytrap (Dionea), native to North Carolina, has an 

 elaborate sensori-motor mechanism for catching its insect-prey and the 

 essentials of a digestive apparatus for preparing it for absorption into 

 the vital juices of the plant. The fly-catcher (Drosophyllum) of Morocco 

 and Portugal and the pitcher-plant so common in New England bogs, 

 catch insects which crawl into them in search of honey or of water by 

 means of glandular hair-like organs that secrete a fluid at once viscid and 



digestive, and make good nutritional 

 use of them. These are but exam- 

 ples of plants which have a true 

 digestion by means of chemical- 

 enzymes '(hydrolyzing agents), while 

 there are many others which in one 

 way or another catch and hold living 

 animals and other sorts of food and 

 absorb the nutritive liquids from 

 them either at once or as they decay. 

 All plants are able to absorb pre- 

 pared carbohydrate and proteid 

 food-substances, but there are many 

 genera that also digest them. 



The Human Digestive Mechanism. 

 A knowledge of the anatomy and 

 histology of the human digestive 

 apparatus is obviously a prerequisite 

 of an understanding of the diges- 

 tion as a process. This information 

 text-books other than those of Phy- 

 siology fully supply, and to them 

 the reader is earnestly referred. 



The mouth or oral cavity is the re- 

 ceptacle into which the food is placed 

 by the hands and the lips, and where 

 it is masticated and insalivated. The 

 tongue is an important organ of 

 digestion, for by it almost alone the 

 food is placed and kept between the 

 two sets of teeth during its masti- 

 cation. It is one of the most versa- 

 tile organs of the body in that it has not only important motor functions, 

 but because it bears also the end-organs of the sense of taste of so great 

 importance in digestion. 



The salivary glands empty their product into the mouth-cavity. Each 

 of them produces to a certain minor extent mixed saliva, although for the 

 most part the product of each is characteristic. The parotid gland is 

 the largest of them, and weighs from 15 to 30 gm. This gland pours 

 its saliva into the mouth through Stenson's duct, which is about 6 cm. 



Alimentary tract of the frog seen from in 

 front: Mh, mouth; Z, extended tongue; S, 

 opening into the larynx, showing the glottis; 

 Oe, esophagus; M, stomach; D, small gut; 

 P, pancreas; L, liver; G, gall-bladder; DC, 

 common place of emptying of the liver and 

 pancreas into the gut; R, large gut; Hb, 

 urinary bladder; Cl, cloaca; A, anus. 

 (Claus.) 



