CONTENTS 



90. What is fermentation and what causes it ? 113 



91. To learn to recognize yeast plants under the compound microscope . 114 



92. Do yeasts grow wild ? . . . . . . . . .115 



93. To determine the conditions favorable to the growth of yeast . . 115 



94. What are the conditions favorable for the growth of yeast in bread ? 



(Home work) 116 



95. How we proceed to the study of bacteria . . . . . .116 



96. How to prepare culture media . 117 



97. To demonstrate a pure culture 118 



98. To determine where bacteria may be found 118 



99. To study how rapidly bacteria grow . . . . . . .119 



100. What foods are preferred by bacteria ?...... 120 



101. What effect has heat upon the growth of bacteria ? 120 



102. To note the effect of moisture and dryness upon the growth of bacteria 



(Home problem) .......... 121 



103. To determine the effect of pasteurization upon the keeping quality of 



milk ' 121 



104. How to care for milk bottles at home ....... 122 



105. To determine the bacterial content of milk 122 



106. To determine some of the most effective preservatives . . .123 



107. To determine the most effective disinfectants 124 



XII. THE RELATIONS OF PLANTS TO ANIMALS . . 127 



108. To study some biological relations of plants and animals in a balanced 



aquarium ........... 127 



109. To learn what we mean by the carbon and the oxygen cycles . . 128 



110. To find out the course of nitrogen in its relation to plants and animals 129 



111. To prove a hay infusion is an unbalanced aquarium . . . .129 



XIII. SINGLE-CELLED ANIMALS CONSIDERED AS ORGANISMS . 132 



112. To study a one-celled animal in order to understand better () its 



reactions to stimuli ; (6) the cell as a unit of structure . . 132 



113. Comparative study of various forms of single-celled animals to explain 



division of labor (Extra problem) 135 



XIV. DIVISION OF LABOR. THE VARIOUS FORMS OF PLANTS AND ANIMALS 137 



114. How the plant kingdom is classified ....... 137 



115. To compare reproduction in plants with that in animals . . . 139 



116. To study the division of labor in tissues and organs .... 140 



117. To find some of the functions common to all animals . . . .141 



118. How to know some types of animals in the animal kingdom . . 141 



XV. THE ECONOMIC IMPORTANCE OF ANIMALS . . 146 



119. What animal foods are cheapest in any locality and why ? (Home 



work) 147 



