Chap. 11 



FOODS AND NUTRITION 



175 



0. I mm 



Fig. 1 1 .4. Didinium nasutum, a microscopic animal, nevertheless a fierce car- 

 nivore. A large Paramecium is attacked by four small Didinia. The Paramecium 

 is torn in pieces and each attacker gets a piece. Or, one Didinium gets the whole 

 Paramecium and forces the others off while it swallows the victim. (Courtesy, 

 Mast, "Reactions of Didinium nasutum," Biological Bulletin 16:100, 1909.) 



human diet includes living plants, living animals, oysters and others; freshly 

 killed animals; and decayed plant and animal tissues. In primitive cultures the 

 latter are inexpensive foods; in more highly cultured circles, decayed foods, 

 among them "high cheese" and mellowed venison are expensive. 



Food Intake by Plants and Animals 



Plants absorb food in solution. Water and salts enter the plant through the 

 root hairs whose delicate surfaces must be constantly moist (Fig. 4.9). Roots 

 turn toward water and stems toward light, but plants hunt only in these ways. 

 Excepting parasites, most land animals and many aquatic ones go from one 

 place to another after food, a continual prowl if they prey on other animals, 

 sometimes a long wandering if they feed on plants. The majority of animals 

 eat solid foods, microscopic particles taken into the food vacuole of an ameba, 

 a whole sheep into the stomach of a great python snake. But before any food 

 is absorbed it must be in solution. 



Feeding Devices. Contraction of protoplasm always figures in the intake of 

 solid food. The protoplasm of an ameba contracts about a diatom. The lashing 

 ciUa of a paramecium or a rotifer create currents that bear processions of 

 microscopic food particles through their mouths and gullets (Fig. 11.5). Cilia 

 bring the food to the mouths of such aquatic animals as the sea anemones, 

 clams and oysters, and the swimming young of starfishes. Certain sizes and 

 shapes of particles are selected by the ciliary currents, often by means of 



