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 
