INTERRELATIONS OF PLANTS AND ANIMALS 133 



Ward, Pure Milk and the Public Health. 



" Miik and its Products as Carriers of Tuberculous Infection." Circular 

 143, Bureau of Animal Industry, U. S. Department of Agriculture, 1909. 



Hall, "The Soil as a Battle Ground." Harper's Magazine, October, 

 1910. 



Weyl, W., " Pure Milk and Human Life." Success Magazine, March, 

 1909. 



Gulick, L. H., "Constructive Community and Personal Hygiene." 

 Science, May 27, 1910. 



Dorset, M., "Some Common Disinfectants." Farmers' Bulletin 345, 

 U. S. Department of Agriculture, 1908. 



I 

 PROBLEM XXIV 



A study of some biological relations of plants and 

 animals. 



a. The Balanced Aquarium (A Food Relation) 



Observations. 1. What have you learned is formed and set 

 free when water-living plants (algae) are exposed to sunlight ? 



2. What do animals need that is commonly obtained from 

 the air ? 



3. Do you think that water animals need the same sub- 

 stance ? If so, where might it come from ? 



4. What gas is given off from the lungs of man ? Note. 

 The same gas is given off by all other animals, by very 

 small animals through the cell wall, by fishes through the gills, 

 etc. 



5. Do plants use this gas ? How do they use it ? 



6. Animals also give off certain nitrogenous wastes, such as 

 urea and ammonia. 



Conclusions. 1. How may the fishes in an aquarium obtain 

 the necessary oxygen for respiration or breathing ? 



2. How might the oxygen get into the water ? 



3. Where might the plants in an aquarium obtain necessary 

 carbon dioxide ? Nitrogenous matter ? 



4. Itemize briefly how the plants and animals of an aqua- 

 rium might be helpful to one another. 



