SMOOTH MUSCLE RESPONSES 
183 
the relaxation phase of the response, as is typically shown in figure 
8. In posterior sections of the frog stomach an accessory res- 
ponse frequently, one could almost say, invariably, could be in- 
itiated on the relaxation of the curve following stimulation. Just 
where on the relaxation phase this secondary response appears is 
variable, sometimes (Fig. 4A) it is near the base, and again it is 
near the top causing a “summation” as in figure 4B. At present 
we are not able to make satisfactory explanation of this phenome- 
non. 
In the case of the effect of resistance on responses, Budington 
in his experiments with the earthworm muscles showed that resis- 
tance when introduced had a decided depressing effect. We find 
in the earthworm a similar condition, as figure 10 shows, that is, 
when various amounts of resistance are introduced, there is a 
marked variation in the height of contraction, this in general being 
proportional in decrease as resistance is increased. Incidentally, 
under the maximum amount of resistance tried (twenty meters 
of German silver wire) where the resulting response is relatively 
small, an introduction of 1.2 per cent ethyl alcohol for thirty 
seconds before stimulation with the same amount of resistance, 
resulted in a contraction approximately ten times greater. On 
being stimulated again, five minutes later, a second response could 
be obtained almost as great. So far as the general type of curve 
produced is concerned it is comparable to the others, hence we 
may interpret that the immediate effect is one of sensitization only. 
Using the frog esophagus and the intestine, relatively similar var- 
iations in the height of the curves were obtained respectively on 
introducing resistance and a resulting sensitization on being sub- 
jected to certain weak strengths of ethyl alcohol as shown in 
figures 7 and 9. 
The diminution in height of responses of earthworm muscle 
due to fatigue and resistance factors is strikingly shown in figure 
12 where alternately twenty meters of resistance, and no resis- 
tance were applied, followed finally by the application of 0.78 per 
cent ethyl alcohol as a sensitizer. The contrasts in heights here 
need no further discussion. Most of our work on the fatigue 
process was concerned with the experiments with the circular 
muscles of the earthworm body, and it is safe to say that like the 
voluntary muscle there is evident the treppe phenomenon wherein 
a gradual accumulation of sensitizations is noticeable, and that 
like the voluntary muscle the latency period is very short. In this 
