Page:Collected Physical Papers.djvu/277

Rh reactions in living tissues, as for example in the physiological action of drugs, which may be regarded as chemical stimuli. A small 'dose' in such cases is often found to give rise to an effect precisely opposite to that produced by a large dose.

Variation of temperature produces a marked effect on the response of muscle. At a low temperature the response is very sluggish and the amplitude of response is very much reduced. With rise of temperature the size of response increases and the period of recovery becomes quickened (fig. 61 a, b). Above a certain optimum the response becomes diminished.

Parallel effects are observed in the response of the inorganic receiver. The curve a to the right represents the response of the magnetic oxide of iron receiver when cold; the deflection was moderate and the recovery was extremely slow. On raising the temperature of the receiver to about 15° C. above that of the room, the amplitude of the response was found to be very much increased—nearly threefold.