CONCLUSIONS 99 



to do by many, but their action is shown by the change 

 in respiration in a manner more perfect than in any 

 other way except by the electrical response. Small 

 amounts of anesthetics at first increase irritability; and 

 at first they increase the rate of respiration and coinci- 

 dently they increase the electrical response. Irritability, 

 respiration, and electrical response parallel each other so 

 completely that they are evidently different aspects of 

 the same thing. 



In chapter v what we had established as being true 

 in the case of nerves was shown to be true in the case 

 of all forms of living matter. Taking the least promising 

 kind of living matter, that of a dry seed, we demonstrated 

 that it, too, breathed as long as it lived, that it 

 produced carbon dioxide, and increased its output 

 of carbon dioxide when it was mechanically stimu- 

 lated by being crushed. Seeds, too, it was shown, 

 could be anesthetized, in which condition they give off 

 less carbon dioxide and no longer respond by an outburst 

 of carbon dioxide when injured. Extending our observa- 

 tions, we found that all kinds of plant and animal tissues, 

 'without any exception, respond in a manner similar to 

 that of the nerve fiber. In all cases stimulation causes 

 an increase in carbon dioxide. We could never find 

 any response unaccompanied by an outburst in car- 

 bon dioxide. Hence the best way to discover whether 

 a tissue is living is to crush it and see whether it reacts 

 to the injury by producing more carbon dioxide. It is 

 not necessary to put seeds in the ground to determine 

 whether they live; by crushing some of them we may 

 discover whether they are alive or not. Thus the 

 chemical test of life in the tissues, a test which parallels 



