Helmholtz' technique was quite simple. He first cut out a muscle and an attached nerve fiber from a frog's leg. The experiment then consisted of stimulating the nerve at various distances from the muscle and measuring the length of time between nerve stimulation and muscle contraction. First, he electrically stimulated the nerve close to the point at which it attaches to the muscle, then he stimulated the nerve farther from this point of attachment. He found that the second reaction time (that is, the time between stimulation and contraction) was longer than the first. To obtain an estimate of the nerve impulse speed, he used a simple bit of reasoning: The difference in time between the two measurements must correspond to the time it takes the nerve impulse to travel the distance between the two points of stimulation (see Fig. 1). Hence, the distance between the point of stimulation divided by the time difference between the conditions of stimulating close to the muscle versus stimulating farther away should yield an estimate of nerve impulse speed. This is how he obtained his estimate of fifty to one hundred meters per second.