BIOLOGICAL INTRODUCTION. 



(e) Take two other specimens, keeping one in the dark, the 

 other in the light. Is there any change in growth ? 



(/) In a sterilized test-tube, place some yeast mixture and boil 

 for several minutes. Replace the sterile cotton plug in the mouth 

 of the tube and set to one side. Examine from time to time. Does 

 growth continue ? 



(g) Taste some fresh yeast mixture. Taste again after the 

 mixture has been in the incubator for twenty-four hours. To 

 what is the difference in taste due? 



(h) Grow some yeast in a tightly stoppered flask, connected, by 

 means of. a bent glass tube, with another flask containing a solu- 

 tion of calcium hydrate. What is the result ? Explain. 



III. PROTOZOA. 



1. Amoeba. These simplest forms of animal life are distin- 

 guished from the simplest plant cells, not so much through their 

 power of locomotion as through a difference in their processes of 

 nutrition. The plant cells, which have been studied in the previ- 

 ous exercises, have been able to build up their living cell substance, 

 protoplasm, a proteid body, out of non-proteid material. This the 

 animal cells, of which the amceba is a type, are unable to do. In 

 other words, the animal cells are dependent upon vegetable cells 

 to manufacture their protein for them. 



4 



FIG. i. Amceba. Phases of amoeboid movement. 



Amceba are commonly found in stagnant pools, mud, and col- 

 lections of water containing decaying vegetable matter. They are 

 seen as minute jelly like masses, with a more or less granular in- 

 terior and a clearer, more transparent peripheral portion (see 

 Fig. i). 



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