XV. THE PROTOZOA 



Problem XXV. The study of a one-celled animal. (Labora- 

 tory Manual, Problem JCJCV.} 

 (a) In its relations to its surroundings. 

 (#) As a cell. (Optional.) 

 (c) In its relations to man. 



We have seen that perhaps the simplest plant would be exem- 

 plified by one of the tiny bacteria we have just read about. A 

 typical one-celled plant, however, would contain green coloring 

 matter or chlorophyll, and would have the power to manufacture 

 its own food under conditions giving it a moderate temperature, 

 a supply of water, oxygen, carbon dioxide, and sunlight. Such a 

 simple plant is the pleurococcus, the " green slime " seen on the 

 shady sides of trees, stones, or city houses. This plant would meet 

 one definition of a cell, as it is a minute mass of protoplasm contain- 

 ing a nucleus. It is surrounded by a wall 1 of a woody material 

 which covers a delicate membrane formed by the activity of 

 the living matter within the cell. It also contains granules of 

 protoplasm colored green, called chloroplasts. Of their part in 

 the manufacture of organic food we have already learned. Such 

 is a simple plant cell. Let us now examine a simple animal cell in 

 order to compare it with that of a plant. 



The Paramcecium. The one-celled animal most frequently 

 found in hay infusions is the paramcecium, or slipper animalcule 

 (so-called because of its shape). 



This cell is elongated, oval, or elliptical in outline, but somewhat 

 flattened. Seen under the low power of the microscope, it 

 appears to be extremely active, rushing about now rapidly, now 

 more slowly, but seemingly always taking a definite course. The 

 more pointed end of the body (the anterior) usually goes first. 



1 This shows one practical reason why plant food often contains more indigestible 

 matter than animal food of same bulk. 



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