PROTOPLASM AND THE CELL 29 



impossible of correct analysis, is nevertheless composed of cer- 

 tain chemical elements which are always present. To this living 

 matter the name protoplasm has been given. 



Protoplasm, then, is made up of certain chemical elements, 

 combined in definite proportions. What is of far more impor- 

 tance to us is the fact that it is distinguished by certain properties 

 which it possesses and which inorganic matter does not possess. 



Properties of Protoplasm. — Plants and animals are largely made 

 up of living matter. Let us study its properties: — 



(1) It responds to influences or stimulation from without its 

 own substance. Both plants and animals are sensitive to touch 

 or stimulation by light, heat, or electricity. Leaves turn toward 

 the source of light. Some animals are attracted to light and 

 pthers repelled by it; the earthworm is an example of the latter. 

 Many other instances might be given. Protoplasm is thus said 

 to be irritable. 



(2) Protoplasm has the power to move and to contract. Muscular 

 movement is a familiar instance of this power. Plants move 

 their leaves and other organs. One-celled animals change thefr form. 



(3) Protoplasm has the power of taking up food materials, of se- 

 lecting the materials which can be used by it, and of rejecting the sub- 

 stances that it cannot use. A commercial sponge, the dried skeleton 

 of an animal, if placed in water, will swell up with the water 

 absorbed by it, but the water thus taken in is not used by the 

 dead skeleton. Protoplasm, however, in the tiny parts of the 

 root of a plant called the root hairs, takes in only the material 

 w^hich will be of use in forming food or new protoplasm for the 

 plant. An animal selects only such food as it wants, and refuses 

 to eat material that it does not use as food. 



(4) Protoplasm grows, not as inorganic objects grow, from the out- 

 side,^ but by a process of taking in food material and then changing 

 it into living material. To do this it is evident that the same 

 chemical elements must enter into the composition of the food 

 substances as are found in living matter. The simplest plants 



^ Experiment. — • Make a strong solution of alum (two spoonfuls of powdered alum 

 to half a glass of water). Suspend in the glass a thread with a pebble attached to 

 the lower end. Notice where and how crystals of alum grow. 



