46 ELEMENTARY ZOOLOGY. 



pond-silk or the wheat or corn may be nourished, through its 

 complete life cycle, by a water-culture in which the necessary 

 inorganic compounds have been supplied in proper proportions 

 together, of course, with atmospheric air without any organic matter 

 whatever. The student will know that these plants ordinarily 

 avail themselves of the decaying organic matter in the soil. 



A demonstration of living bacteria should be made 

 under the highest power of the microscope, and the odor 

 of the solution in which they are found should be noted. 

 What does the odor indicate? Why does not meat, 

 which has been properly canned, have this odor? 



Similarly, the habits of the molds and their effect on 

 the bread should be studied. Where have you seen 

 molds in nature? Enumerate all the substances on 

 which you have seen them growing. What kind of 

 substances are they? Have you any evidence that the 

 mold is actually disorganizing the bread? Is it fair to 

 infer that it uses the bread in its growth? How would 

 you test whether the mold actually must have organic 

 food? Have such tests ever been made? 



In a similar spirit study the food necessities of all the 

 organisms under consideration, and state clearly the 

 facts. 



60. Compare all the forms that you have classed under 

 group i; similarly those of group 2. Have the I's any- 

 thing in common, of structure or appearance, other than 

 this food requirement? Have the 2's? 



6 1. A Second Classification of Organisms. Organisms 

 are commonly classed as : 



A. Plants. 



B. Animals. 



To which of these groups do the various organisms 

 you have been studying belong? 



