A few sample results showing the influence of the whistle upon a small bull-frog follow:
| Length of 10 Resps. Before Stimulus in cm. | Length of 10 Resps. After Stimulus in cm. | ||
|---|---|---|---|
| 1st | Stim. | 6.0 | 6.7 |
| 2d | " | 5.4 | 6.0 |
| 3d | " | 5.9 | 5.8 |
| 1st | " | 4.7 | 5.4 |
| 2d | " | 4.4 | 4.6 |
As a test-check observation for comparison, the influence of a visual stimulus upon respiration was noted under the same conditions as for the auditory. Effect of turning on electric light over box.
| Length in cm. of 10 Resps. Before Stimulus. | Length in cm. of 10 Resps. After Stimulus. |
|---|---|
| 4.8 | 4.4 |
| 5.3 | 4.6 |
| 4.5 | 4.0 |
These results indicate an increase in the respiration rate due to the visual stimulus.
4. Of the other auditory stimuli used, the pistol-cap explosion gave very irregular results. For one animal it caused acceleration, for another inhibition. There is, however, good evidence that the sounds were heard.
5. The ringing of a bell gave results similer to those for a whistle, and the sound of a 500 S.V. tuning fork usually caused a slight increase in the rate of breathing. In these experiments I therefore have evidence, through their effects upon respiration, of the frog's ability to hear sounds ranging from 50 V. to at least 1,000 V.
The croak of the green frog ranges from 100 to 200 V., so far as I have been able to determine. That of the bull frog is lower, from 50 to 75; and in the leopard frog the range is from 80 to 125. The latter is very different from the green frog in its croaking, in that it croaks whenever disturbed, whereas, the green frog rarely responds in that way to a stimulus.
We are now in a position to say that the failure of frogs to give motor reactions to strong auditory stimuli is not due to their inability to be affected by the stimuli, but is a genuine inhibition phenomenon.