PART II. ZOOLOGY 



XII. PROTOZOA 



A Hay Infusion. — The smallest and simplest plants studied 

 were composed of a single cell; the simplest animals are likewise 

 composed of but one cell. Place a wisp of hay or straw in a small 

 glass jar nearly full of water, and leave it for a few days in a warm 

 room. Certain changes are seen to take place in the contents of 

 the jar; the water after a little gets cloudy and darker in color; a 

 scum appears on the surface, which is made up of bacteria. These 

 bacteria evidently aid in the decay which (as the unpleasant odor 

 from the jar testifies) is taking place. Later, small one-celled 

 animals appear; these multiply with wonderful rapidity, so that 

 in some cases the surface of the water seems to be almost white 

 with active one-celled forms of life. If we ask ourselves where 

 these animals come from, we are forced to the conclusion that 

 they must have been in the water, the air, or the hay. Hay is 

 dried grass, which may have been cut in a field near a pool con- 

 taining these creatures. When these pools dried up, the wind may 

 have scattered some of these little organisms in the dried mud or 

 dust. Some may exist in a dormant state on the hay, the water 

 serving to awaken them to active life. In the water too there 

 may have been some living cells, plant and animal. In the decay- 

 ing hay and in water are cell food in abundance, both inorganic 

 and organic. Living cells increase rapidly here because of the 

 favorable conditions under which they exist. This combination 

 of living and dead matter just described is called a hay infusion. 



Study of the Paramcecium.} — Let us now take up the study of one of these 

 simple one-celled animals found in a hay infusion. For this purpose the 

 compound microscope, slides, coverslips, a little powdered carmine, and an 

 infusion containing paramoecia are necessary. Paramoecia usually appear in 

 a hay infusion in three or four days. 



The form of the paramcecium, or slipper animalcule, as it is sometimes 

 called, is elongated, oval in outline, and somewhat flattened. Notice that 



^ Hunter and Valentine, Manual, page 163. 



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