I40 
Horseshoe crab. See Limulus 
polyphemus. 
Hydrogen, 26, 60; decreased 
metabolism in 44; lack of in- 
creased metabolism in, 44. 
Hydrolysis, 52. 
Hypoglossal nerve. See Nerve. 
Impulse: in plant, 2; nerve, see 
Nerve impulse. 
Inhibition: by heat, 58; 
transmissibility of, 58. 
Injury, 41, 91. 
Insect, wings of, 47. 
Invertebrate, 18. 
Irritable response, 103. 
Irritability: definition of, 4; 
metabolic condition for, 85; 
nature of, 104; origin of physi- 
cal theory of, 9; relation of, to 
conductivity, 57; relation of, to 
metabolism, 104; two phases in 
protoplasmic, 57. 
non- 
Katabolism, 48. 
King crab. See Limulus poly- 
phemus. 
Lateral line nerve. See Nave. 
Lavoisier, 11. 
Learning, phenomenon of, 35. 
Lens, 15, 16. 
Libinia canaliculata. 
dioxide production. 
Life: chemical sign of, chap. v; 
definition of, 95; quantity of, 
107. 
Light, 35. 
Limax, 22. 
Limulus. See Limulus polyphemus. 
See Carbon 
Limulus polyphemus. See Carbon 
dioxide production. 
Living process, 103; material 
changes in, 3; physical state of, 
105. 
Living things: property of, 3; two 
signs of, 4. 
Lobster. See Homarus vulgaris. 
A CHEMICAL SIGN OF LIFE 
Man. See Carbon dioxide pro- 
duction. 
Mathews, 35, 41. 
Mayer, 82. 
Mayow, 11. 
Medullary sheath, 51, 58; func- 
tion of, 18. 
Medullated nerve, 18, 21. See 
also Carbon dioxide production. 
Memory, 35. 
Metabolic gradient. See 
dient. 
Metabolism: function of, 85, 104; 
increased, on stimulation, 34; 
in different tissues and organ- 
isms, see Carbon dioxide pro- 
duction; indirect evidence for, 
in nerve, 12; its meaning, 50, 
104; method of study of, in 
nerve, see Biometer; relation to 
behavior, 81; resting, 33, 89. 
Methylene blue, 37. 
Motor nerve. See Nerve. 
Mouse, 22. 
Muscle: acid production in, 91; 
contraction of, as sign of nerve 
impulse, 23; Increased metab- 
olism of contracting, 35; 
smooth, 51; voluntary, 18. 
Gra- 
Narcosis. See Anesthesia. 
Narcotics. See Anesthetics. 
Negative phase, 13. 
Negative response, influence of 
carbon dioxide, 14. 
Nerve: afferent, 58; claw, 18; 
efferent, 58; hypoglossal, 79; 
lateral line, 22; motor, 21; 
oculomotor, 21; olfactory, 21; 
optic, 22; sciatic, 21, 22, 67; 
sensory, 22, 58; nerves of 
different animals. See also 
Carbon dioxide production. 
Nerve fibers: Changes of weight 
under anesthesia, 62, 65; chem- 
ical change in, chaps. ii and iii; 
chemical sign of, 55; different 
