DuBois-Reymond's law deals with

• A. Rheobase
• B. Chronaxie
• C. Intensity of stimulus
• D. Make-break law

Answer: (C)

Du Bois-Reymond’s observation centers on how nerve fibers respond to the strength of an electrical stimulus. He showed that excitation depends on reaching a certain stimulus intensity: when the current is strong enough, the nerve fires; as the intensity increases, the likelihood and strength of the response grow. This focus on how the strength of the stimulus drives activation is why intensity of stimulus is the best fit.

Rheobase and chronaxie are concepts that come from the strength-duration relationship: rheobase is the minimum current needed if the pulse is very long, and chronaxie is the minimum time needed for a current equal to twice the rheobase to elicit a response. Make-break law deals with how nerves respond to on-off (pulse) stimulation. These involve duration and delivery of the stimulus, not the fundamental emphasis on stimulus strength that Du Bois-Reymond highlighted.