22 A CHEMICAL SIGN OF LIFE 
3. MEDULLATED NeERvVEs: Sciatic: nerve of the dog, frog, 
turtle, mouse, guinea-pig; optic nerve of the skate (both 
Raia ocallata and Raia ecrinecia). 
4. Non-MeEpULLATED Nerves: Nerves of the spider crab, 
olfactory nerve of the skate (Raia ocallata). 
5. NERVES OF INVERTEBRATES: Nerves of the spider crab, 
Limulus, Limax. 
6. NERVES OF VERTEBRATES: Nerves of frog, dog, mouse, 
squiteague (Cynoscion regalis), and skate (both Raia 
ocallata and Raia erinecia). ° 
7. NERVES OF WarM-BLOoDED ANIMALS: Those of dog, rat, 
rabbit, guinea-pig. 
8. NERVES OF CoLD-BLoopED Animats: Those of frog, squi- 
teague (Cynoscion regalis), catfish, carp, and skate. 
9. SENSORY Denprite: Lateral line nerve (ramus lateralis 
vagi) of carp and catfish, and ramus lateralis accessorius of 
catfish. 
This is a partial list of the many nerves examined and 
it is given only to show that we are justified in making 
the generalization that all freshly isolated nerves of 
all animals, regardless of the kind of nerve or of the kind 
of animal, produce carbon dioxide. It is thus certain 
that chemical changes of a very vigorous kind are 
going on constantly in this tissue without any visible 
results. Nerves respire; they are not chemically inert. 
It remains now for us to establish the fact that this car- 
bon dioxide is a product of normal metabolic activity 
and is not due to a disintegration involved in the process 
of dying on the part of the tissue, or to a lifeless fermen- 
tation, and that it is not simply gas which had happened 
to be absorbed by the nerve from the atmosphere or the 
blood. 
Is this carbon dioxide produced by living processes ?— 
Since there are many organic compounds, as well as dead 
