CHEMICAL SIGNS OF IRRITABILITY 21 



Thus, since we know the original volume of the chamber in 

 which the respiration took place and from which this minimum 

 volume is withdrawn, and since we know the quantity of carbon 

 dioxide contained in this volume, it is easily calculated how 

 much carbon dioxide is given off by the nerve during the known 

 period. It should be understood that, in determining the mini- 

 mum volume of gas taken from the respiratory chamber, a series 

 of experiments was conducted in order to calculate both the mini- 

 mum volume which just gives the precipitate and the maximum 

 volume which does not give the precipitate for a known weight of 

 the nerve for a known period of respiration. In Table I, in the 

 Appendix (p. 128), columns 8 and 9 refer to these volumes 

 calculated from experiments for 10 mg. of the nerve, for ten 

 minutes. 



Medullated nerve fibers. We have repeated this 

 experiment with the sciatic nerve of the frog, this nerve 

 being a typical medullated nerve. The result showed, 

 not only that medullated nerves also give off carbon 

 dioxide, but that they give a quantity of about 5 . 5 X 

 io~ 7 g. for each 10 mg. of the nerve for the first ten 

 minutes, which is a little less than was obtained from 

 the non-medullated nerve. 



A large variety of nerves was tested to see whether or 

 not all resting nerves give off carbon dioxide. As a 

 result, we found no exception in any of them, although 

 they vary quite widely in the rate at which they 

 produce carbon dioxide. The following nerves were 

 examined, and it will be noticed that the list includes 

 all varieties, such as sensory, motor, vertebrate and 

 invertebrate, medullated and non-medullated nerves. 



1. MOTOR NERVE: Oculomotor nerve of the skate (Raia 

 ocallata). 



2. SENSORY NERVE: Olfactory nerve of the same. 



