48 A CHEMICAL SIGN OF LIFE 
the nerve has recovered from the first. This refractory 
period of 1/5,000 of a second may be considerably pro- 
longed under certain conditions, such as low temperature, 
high temperature, asphyxiation, various drugs, and 
certain anesthetics. Frélich prolonged this refractory 
period by partial anesthesia and succeeded in producing 
fatigue phenomena by repeated electrical stimulations 
at shorter intervals than the prolonged refractory period 
of the nerve. 
The idea that all the physiological activities are 
composed of at least two opposing metabolic phenomena 
was expressed by Claude Barnard and later extended by 
Hering. Thus metabolic activities are considered as 
consisting of two phases, namely, a breaking down, or 
katabolic, and a building up, or anabolic, phase. That 
two such phenomena are involved in nervous metabolism 
and are closely connected with the phenomena of fatigue 
may be shown by the use of certain drugs in connection 
with electrical changes and refractory periods. Waller 
observed that protoveratrin slows up one of the electrical 
changes (positive variation) of the nerve, while the 
other (negative variation) is little influenced. He 
contended accordingly that this drug does not alter 
katabolic changes of the nervous metabolism but re- 
tards the anabolic activity to a considerable degree. It 
is by its anabolism that the nerve is restored to its nor- 
mal state after the passage of the impulse. Since the 
pharmacological action of protoveratrin and yohimbin 
on muscle are known to be very similar, Tait concludes 
from the study of the effect of yohimbin on the refractory 
period of the nerve that these drugs must attack nerves 
in a similar manner. Yohimbin, in other words, retards 
