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The cutaneous nerves of the frog are extremely sensitive to acids; so I put a drop of acetic acid on the outside of one knee. This, you see, gives rise to most violent movements both of arms and legs, and notice particularly that the animal is using the toes of the leg on the same side for the purpose of rubbing the irritated spot. I dip the whole animal into water in order to wash away the acid, and now it is all at rest again. . . . I put a drop of acid on the skin over the lumbar region of the spine. . . . Both feet are instantly raised to the irritated spot. The animal is able to localize the seat of irritation. . . . I wash the acid from the back, and I amputate one of the feet at the ankle. . . . I apply a drop of acid over the knee of the footless leg. . . . Again, the animal turns the leg towards the knee, as if to reach the irritated spot with the toes; these, however, are not now available. But watch the other foot. The foot of the other leg is now being used to rub away the acid. The animal, finding that the object is not accomplished with the foot of the same side, uses the other one.

I think that at least one thing will be patent to every unprejudiced reader of these excerpts, namely–that any frog (with its head on or its head off) which happened to make the personal acquaintance of Professor Rutherford must have found him poor company. What benefit science may have derived from such association I am not qualified to pronounce upon. The lecturer showed conclusively that the frog is a peculiarly sensitive and intelligent little batrachian. I hope that the genial professor, in the years which followed, did not frequently consider it necessary to demonstrate the fact.