[11] Steiner, J.:  ’Untersuchungen ueber die Physiologie des
   Froschhirns.’  Braunschweig, 1885, 127 S.

   [12] Schrader, M.G.:  ‘Zur Physiologie des Froschgehirns.’
   Pflueger’s Arch., Bd. 41, 1887, S. 75-90.

   [13] Merzbacher, L.:  ’Ueber die Beziebungen der Sinnesorgane zu
   den Reflexbewegungen des Frosches.’ Pflueger’s Arch., Bd. 81,
   1900, S. 223-262.

   [14] Merzbacher, L.:  ’Untersuchungen ueber die Regulation der
   Bewegungen der Wirbelthiere.  I. Beobachtungen an Froeschen.’
   Pflueger’s Arch., Bd. 88, 1901, S. 453-474, 11 Text-figuren.

In the present investigation it has been my purpose to study the reactions of the normal frog by the reaction-time methods of the psychologist.  Hitherto the amount of work done, the extent of movements or some other change has been taken as a measure of the influence of a stimulus.  My problem is, What are the time relations of all these reactions?  With this problem in mind I enter upon the following program:  (1) Determination of reaction time to electrical stimuli:  (a) qualitative, (b) quantitative, (c) for different strengths of current; (2) Determination of reaction time to tactual stimuli (with the same variations); (3) Auditory:  (a) qualitative, (b) quantitative, with studies on the sense of hearing; (4) Visual:  (a) qualitative, (b) quantitative, with observations concerning the importance of this sense in the life of the frog, and (5) Olfactory:  (a) qualitative, (b) quantitative.

The present paper presents in rather bare form the results thus far obtained on electrical, tactual, and auditory reaction time; discussion of them will be deferred until a comparison of the results for the five kinds of stimuli can be given.

V. METHOD OF STUDY.

The measurements of reaction time herein considered were made with the Hipp Chronoscope.  Cattell’s ‘Falling Screen’ or ‘Gravity Chronoscope’ was used as a control for the Hipp.  The Gravity Chronoscope consists of a heavy metal plate which slides easily between two vertical posts, with electrical connections so arranged that the plate, when released from the magnet at the top of the apparatus, in its fall, at a certain point breaks an electric circuit and at another point further down makes the same circuit.  The rate of fall of the plate is so nearly constant that this instrument furnishes an accurate standard time with which Hipp readings may be compared, and in accordance with which the Hipp may be regulated.  For, since the rate of a chronoscope varies with the strength of the current in use, with the variations in temperature and with the positions of the springs on the magnetic bar, it is always necessary to have some standard for corrections.  In these experiments the time of fall of the gravity chronoscope plate, as determined by the graphic method with a 500 S.V. electric tuning fork, was 125[sigma] (i.e., thousandths of a second).