Then, too, in the study of animals the relation of reaction time to instincts, habits, and the surroundings of the subject are to be noted.  Variability and adaptability offer chances for extended biological inquiries; and it is from just such investigations as these that biology has reason to expect much.  The development of activity, the relation of reflex action to instinctive, of impulsive to volitional, and the value of all to the organism, should be made clear by reaction-time study.  Such are a few of the broad lines of inquiry which are before the comparative student of animal reaction time.  It is useless to dwell upon the possibilities and difficulties of the work, they will be recognized by all who are familiar with the results of human studies.

In the study of the time relations of neural processes Helmholtz was the pioneer.  By him, in 1850, the rate of transmission of the nerve impulse in the sciatic nerve of the frog was found to be about 27 meters per second[4].  Later Exner[5] studied the time occupied by various processes in the nervous system of the frog by stimulating the exposed brain in different regions and noting the time which intervened before a contraction of the gastrocnemius in each case.  Further investigation of the frog’s reflex reaction time has been made by Wundt[6], Krawzoff and Langendorff[7], Wilson[8] and others, but in no case has the method of study been that of the psychologist.  Most of the work has been done by physiologists who relied upon vivisectional methods.  The general physiology of the nervous system of the frog has been very thoroughly worked up and the papers of Sanders-Ezn[9], Goltz[10] Steiner[11] Schrader[12] and Merzbacher[13],[14] furnish an excellent basis for the interpretation of the results of the reaction-time studies.

   [4] Helmholtz, H.:  ’Vorlaeufiger Bericht ueber die
   Portpflanzungsgeschwindigkeit der Nervenreizung.’ Arch. f. 
   Anal. u.  Physiol., 1850, S. 71-73.

   [5] Exner, S.:  ’Experimentelle Untersuchung der einfachsten
   psychischen Processe.’ Pflueger’s Arch., Bd. 8. 1874, S.
   526-537.

   [6] Wundt, W.:  ’Untersuchungen zur Mechanik der Nerven und
   Nervencentren.’  Stuttgart, 1876.

   [7] Krawzoff, L., und Langendorff, O.:  ’Zur elektrischen
   Reizung des Froschgehirns.’ Arch. f.  Anal. u.  Physiol.,
   Physiol.  Abth., 1879, S. 90-94.

   [8] Wilson, W.H.:  ’Note on the Time Relations of Stimulation of
   the Optic Lobes of the Frog.’Jour. of Physiol., Vol.  XI.,
   1890, pp. 504-508.

[9] Sanders-Ezn:  ’Vorarbeit fuer die Erforschung des Reflexmechanismus in Lendentmark des Frosches.’ Berichte ueber die Verhandlungen der Kgl. saechs.  Gesellsch. d.  Wissensch. zu Leipzig, 1867, S. 3.

   [10] Goltz, F.:  ’Beitraege zur Lehre von den Functionen der
   Nervencentren des Frosches.’  Berlin, 1869, 130 S.