42 FOUNDATIONS OF BIOLOGY 



1. Food Taking 



The food of Paramecium is chiefly microscopic, colorless 

 plants known as BACTERIA which are present in countless 

 numbers in decaying vegetable infusions. As Paramecium 

 swims about by means of its cilia, a current of water laden 

 with Bacteria is whirled down the peristome on one side of 

 the animal and some passes through the mouth and gullet 

 into the endoplasm. Here the Bacteria, surrounded by a 

 droplet of water, form a gastric vacuole, into which the endo- 

 plasm secretes chemical substances (enzymes, etc.) which 

 gradually break down that is, digest the complex 

 proteins, carbohydrates, etc., of the plant cells. Finally, 

 this material which shortly before was Bacteria protoplasm 

 is incorporated into Paramecium protoplasm matter and 

 energy is supplied and the animal lives and grows. 



This is, in most regards, a strikingly different condition 

 from that which we have seen in Sphaerella. In Paramecium 

 solid particles of food Bacteria are taken into the cell, 

 and since the chief organic constituents of protoplasm are^ 

 proteins, associated with carbohydrates and fats, it is clear 

 that the income of the animal organism is, unlike that of the 

 green plant, chiefly ready-made complex foodstuffs. In 

 other words, Paramecium, like all animals, requires 

 relatively complex chemical compounds rich in potential 

 energy: proteins, carbohydrates, and fats. Of these, pro- 

 teins or their constituent amino acids are absolutely indis- 

 pensable because it is only from this source that nitrogen 

 is available for the animal. But the green plant, through 

 its chlorophyll apparatus, is able to take materials largely 

 devoid of energy and to rearrange them and endow them' 

 with potential energy which it has received in the kinetic 

 form from sunlight. 



