16 



INTRODUCTION 



Fig. 3. Amoeba in eight successive stages 

 of movement. 



DEMONSTRATIONS AND EXPERIMENTS 1 



1. Amoeba. The amoeba is not always easily obtained. If debris 

 of water plants be kept in shallow dishes of water for several days, 

 there can usually be found specimens of amoeba in the scum that 



forms on the surface of 

 the water, or in the 

 ooze that collects at the 

 edges and bottoms of 

 the dishes. On mount- 

 ing some of the material 

 on a glass slide and ex- 

 amining with the com- 

 pound microscope, there 

 may be seen small, irreg- 

 ular, transparent masses 

 of a jellylike nature 

 moving along very slowly with a rolling or flowing motion (Fig. 3). 

 Attention should be given to the constantly changing form of the 

 animal, which thus exhibits a fundamental characteristic of proto- 

 plasm, instability. If, when an amoeba is fully extended, sending out 

 processes, pxeudopodia, from the main part of the body, the slide be 

 gently tapped, the animal will be seen to contract quickly into a 

 rounded mass, showing another characteristic of protoplasm, irritability, 

 or the capacity of response to stimulus. 



2. White Blood Corpuscles. If a drop of fresh human blood, or 

 preferably of frog's blood, be mount- 

 ed on a glass slide and examined 



with the compound microscope, 



among the numerous red corpuscles 



may be seen a few transparent ones 



(Fig. 4). On remaining undisturbed 



for some time they change in shape, Rg 4 ._ Blood ce ii B (corpuscles) 



or even migrate, in a manner similar of frog. 



1 Note to Teachers. The demonstrations and experiments should 

 precede the recitation of the lessons which they illustrate. The pupil 

 should not be required to describe the brain, for example, until he has 

 studied the dissected organ itself. 



