Soon the _Weber_ as well as the _Fechner_ law had been extended over the whole field of sensation and stimulation. In this connection _Preyer_[24] has formulated his “myophysical law,” which states that there is the same relation between strength of stimulus and the intensity of response of the muscle as is laid down by the _Fechner_ law for stimulation and sensation. _Pfeffer_[25] has found that _Weber’s_ law applied also to the relations of the chemotaxis of bacteria, to the intensity of the chemical stimulus, and likewise the attempt has been made to show that all living substances respond in the manner laid down by the _Weber-Fechner law_. Unfortunately the innumerable investigations in this field have shown more and more clearly that it is not possible to formulate a general mathematical law, which strictly fixes the relations of the intensity of the stimulus and the intensity of response. Even in the field of the physiology of the special senses many voices have opposed the general application of the _Weber_ and the _Fechner law_. _Lotze_, _G. Meissner_, _Dohrn_, _Hering_, _Biedermann_ and _Löwitt_, _Funke_ and numerous other investigators have already demonstrated for some decades, partly by means of critical inquiry, partly by experimentation, that these laws are not strictly valid. Above all these experiments have shown that logarithmic relations are not tenable and likewise are not applicable to very strong stimuli. The assumption made by _Fechner_, that is, the acceptance that all barely perceptible increases of sensation have an equal value, has been set aside as incorrect, and with this his mathematical formulation within those boundaries of intensity of the stimulus, in which the _Weber_ law has proven itself valid, must also be abandoned. That which we can say today with certainty concerning the relation between the intensity of stimulus and the amount of response is as follows: A law generally applicable to the relation between the strength of the stimulus and the amount of response cannot be mathematically formulated. For a great number of living systems the rule which holds for the intensity of stimulation within certain boundaries is the following: With increase of the intensity of stimulation the _response_ at first increases rapidly and later more and more slowly. [24] _Preyer_: “Das myophysische Gesetz.” Jena 1874. [25] _Pfeffer_: “Ueber chemotaktische Bewegungen von Bacterien, Flagellaten und Volvocineen.” Untersuchungen aus dem botanischen Institut zu Tübingen. Bd. II, 1888.