22 A CHEMICAL SIGN OF LIFE 



3. MEDULLATED NERVES: Sciatic nerve of the dog, frog, 

 turtle, mouse, guinea-pig; optic nerve of the skate (both 

 Raia ocallata and Raia erinecia) . 



4. NON-MEDULLATED NERVES: Nerves of the spider crab, 

 olfactory nerve of the skate (Raia ocallata) . 



5. NERVES or 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-BLOODED ANIMALS: Those of frog, squi- 

 teague (Cynoscion regalis), catfish, carp, and skate. 



9. SENSORY DENDRITE: 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 



