III. PHYSICAL NATURE OF ANIMAL LIGHT 40 Purkinje phenomenon. Color and spectra of animal light. Polarization. Efficiency of animal light. Infra-red radiation. Ultra-violet radiation. Luminous efficiency and visual sensibility. Production of radiation penetrating opaque objects. Intensity of animal light. Summary. IV. STRUCTURE OF LUMINOUS ORGANS 67 Photochemical and chemiphotic changes. The eye and the luminous organ. Intracellular and extracellular luminescence. Continuous and intermittent luminescence. Periodicity of luminescence. Luminous bacteria. _Noctiluca_ and photogenic granules. _Chætopterus_ and luminous gland cells. _Cypridina._ Luminous glands. The firefly. Luminous organs (photophores) with lenses, reflectors, opaque and color screens. Uses and purpose of animal light. V. THE CHEMISTRY OF LIGHT PRODUCTION, PART I 85 Boyle's and Spallanzani's experiments. Shining wood and burning coal. Oxygen and luminescence. Carbon dioxide and luminescence. Heat production during luminescence. Luminescence and respiration. Water and luminescence. Phipson's noctilucin. Luciferin and luciferase. Photogenin and photophelein. Proluciferin. Oxyluciferin. Pyrophorin or luciferescein. Chemiluminescent reactions. "Biozymoöxyluminescence." VI. THE CHEMISTRY OF LIGHT PRODUCTION, PART II 114 _Pyrophorus_ luciferin and luciferase. _Pholas_ luciferin and luciferase. _Cypridina_ luciferin; stability, hydrolysis by acid and enzymes, adsorption, precipitation, salting out, solubility, distribution. _Cypridina_ luciferin a proteose? _Cypridina_ luciferase and properties. _Cypridina_ luciferase an albumin. Specificity of luciferase. Action of fat solvent anæsthetics. Action of cyanides. Oxyluciferin. Nature of oxidative reaction. VII. DYNAMICS OF LUMINESCENCE 143 Minute amounts of material for luminescence. Reaction velocity and chemiluminescence. Temperature and chemiluminescence. Oxidation in steps. Concentration and bioluminescence. Temperature and bioluminescence. Oxidation with and without luciferase. Reaction velocity and color of bioluminescence. * * * * * THE NATURE OF ANIMAL LIGHT CHAPTER I LIGHT-PRODUCING ORGANISMS