has become of importance in the discussion of the specific energy of the living substance, is in consequence of the theoretical interest, resulting from its connection with the nature of the specific energy of our _sense substances_. The controversies on this subject are still far from settled.[46] Indeed, according to the special philosophical standpoint taken by an observer, the existence of a specific energy of the senses is acknowledged or disputed. For any one acquainted with the general physiological reaction to stimuli, such a discussion is wholly without purport. The sense substances have as a matter of course in common with all living substances their specific energy, that is, the influence of stimuli can produce an increase or decrease of their specific vital processes. “Specific energy” of “sense substance” in this sense is like that of all other living substances, a fact. In that the psychical capability of these sense substances, in which we include not only the peripheral, but also the central portion, are dependent upon their specific vital processes, it must be self-evident that the excitation and the suppression of sense sensation can be brought about by adequate and inadequate stimuli, no matter what one may think of the relations between physical and psychical phenomena. [44] _Cremer_: “Die allgemeine Physiologie der Nerven.” In Nagels Handbuch der Physiologie des Menschen. Bd. IV, Braunschweig 1909. [45] In the first edition of my “_General Physiology_” in 1895 I have sharply and clearly defined it as such, stating in formulating the general law of stimulation: that every excitation is an increase either of individual parts or the whole of vital phenomena, depression every decrease in the individual part or the whole of vital phenomena. [46] Compare: _Rudolf Weinmann_: “Die Lehre von den specifischen Sinnesenergien.” Hamburg 1895. Further: _Eugen Minkowski_: “Zur Müllerschen Lehre von den specifischen Sinnesenergien.” In Zeitschrift f. Sinnesphysiologie, Bd. 45, 1911. The only debatable question is that concerning the limits of the validity of the doctrine of the specific energy of living substances. This question will involve our attention when we have analyzed somewhat more closely the happenings in the living substance taking place under the influence of stimuli. We will, therefore, return later on to a more detailed consideration of the last question. Nevertheless, we will here refer to a fact which, upon a superficial observation, seems to restrict the validity of the conception of the specific energy of living substance.