CHEMICAL SIGNS OF IRRITABILITY 29 



parallelism between the decrease in metabolism and 

 decrease of irritability in the nerve. The gas produc- 

 tion slows up as the nerve approaches death. This 

 indicates, also, that the carbon dioxide is formed by a 

 vital process. 



Comparison between the metabolism of resting nerves 

 and other tissues. While a comparison of the rate of the 

 metabolism of the nerve with that of other tissues is 

 subject to a good many limitations, since there are so 

 many and great variations in conditions which do not 

 affect all tissues similarly, it is nevertheless interesting 

 to note whether the nerve respires relatively more or less 

 than most other tissues. In order to give a better 

 numerical picture of the amount of metabolism in the 

 resting nerve, as compared with other tissues, we have 

 set down in Table III the figures for carbon dioxide 

 production in various animals. Since there are no exact 

 determinations made of the carbon dioxide production of 

 the spider crab as a whole, or of its tissues, we have used 

 for comparison various other Crustacea where these 

 data have been determined. It will be noticed from an 

 inspection of this table that the spider crab nerve pro- 

 duces, weight for weight, carbon dioxide at a rate three 

 to four times that of the whole body of crabs, and almost 

 as much in proportion to weight as a human being at 

 rest. Recently Bayliss, in his admirable book entitled 

 Principles of General Physiology, expressed a doubt of our 

 figures. He thinks that the gas we measured must be 

 due to some cause other than the metabolic activity of 

 the nerve, because, he says, the data show that it is 

 greater than that of an equal weight of muscle. It is 

 rather difficult for us to understand the force of this 



