40 EXPERIMENTAL PHYSIOLOGY 



the round spots in the cytoplasm (vacuoles: food vacuoles, 

 water vacuoles, or contractile vacuoles, according to con- 

 tents) ; the constantly forming projections of the cytoplasm 

 (pseudopodia) ; and the absence of any cell wall. 



(Amoeba is a one-celled animal made up of free protoplasm 

 and hence well suited to show the properties of this sub- 

 stance, which is the physical basis of all life.) 



Properties of Protoplasm. 



A. What color is the cytoplasm? Does it appear thicker 

 or thinner than the water? Is the part containing granules 

 of the same color as the clear part? Does this cytoplasm 

 mix with the water? Describe the appearance of the nu- 

 cleus. 



B. Movement. Watch the moving amoeba. Note the va- 

 rious steps in the forming of a pseudopodium. Is the move- 

 ment of the animal rapid? Does it appear to move in a 

 definite direction or at random? Do the particles in the 

 water appear to affect its movement? Press on the cover 

 glass with a needle point just above the amoeba. How does 

 the amoeba react? Note that the movement of the amoeba 

 is produced as a result of two properties of protoplasm, 

 contraction and expansion. A substance having these prop- 

 erties is said to have contractility. 



C. In B we noted that the animal contracted and ex- 

 panded without apparent cause in some cases. We noted 

 also that under pressure it contracted more strongly. This 

 power to respond to special stimuli is called irritability. 

 Test the irritability of the protoplasm toward heat, by ap- 

 plying the flame of an alcohol lamp gently to the end of 

 the glass slide. Record your observations as the heat grad- 



