xii CONTENTS 



I'A(,E 



The Colloidal State - 176 



Colloidal Gold - 176 



Emulsoids - 177 



Swelling - 177 



Surface Tension and Dispersion 177 



Electrical Charge 177 



Artion of Electrolytes - 178 



Mutual Precipitation 179 



Staining and Electrical Adsorption i"v 



Rate of Reaction between Colloids - 179 



CHAPTER II 



Chemical Composition of Organisms 181 



The Polarimeter - 181 



Waste Products 182 



Carbon Cycle 183 



Water Culture - 183 



Action of Green Plant on Carbon Dioxide 183 



Chlorophyll 186 



Formation of Starch - 186 



The Nitrogen Cycle 186 



Bacteria 186 



Formation of Nitrates in the Soil 186 



Root Nodules - 187 



Salts 187 



Sources of Energy 189 



Alimentary Canal of Frog and Rabbit 189 



Enzymes and Digestion 189 



Rates of Reactions 189 



Hydrolysis'by Enzymes 190 



Enzymes Act at their Surfaces 192 



Catalytic Action 192 



Model 192 



Various Digestive Enzymes 193 



Amylase - 193 



Invertase - 193 



Pepsin 193 



Trypsin - 193 



Absorption - 193 



Histological Preparations 193 



Voluntary and Involuntary Muscle 195 



Contractions of the Frog's Stomach 196 



Secretion - 196 



Pancreas - 196 



Living Newt's Stomach 196 



Flow of Water - 197 



Electrical Change 197 



Respiration - 200 



Trachea? of Insect 200 



Haemoglobin as Oxygen Carrier 200 



Absorption Spectrum of Hitmoglobin - 201 



Carriage of Carbon Dioxide 201 



Stimulation of Respiration by Carbon Dioxide 202 



