1. The green frog is very timid and does not respond normally to most stimuli when in the presence of any strange object. Fright tends to inhibit movement.
2. That it is able to profit by experience has been proved by testing it in simple labyrinths. A few experiences suffice for the formation of simple associations; but in case of a series of associations from fifty to a hundred experiences are needed for the formation of a perfect habit.
3. Experiment shows that the frog is able to associate two kinds of stimuli, e.g., the peculiar tactual stimulus given by a wire and a painful electric stimulus which in the experiments followed the tactual. In this case the animal learns to jump away, upon receiving the tactual stimulus, before the experimenter gives the electric stimulus.
4. Vision, touch and the organic sensations (dependent upon direction of turning) are the chief sensory factors in the associations. The animals discriminate colors to some extent.
5. Perfectly formed habits are hard to change.
6. Fear interferes with the formation of associations.
7. Associations persist for at least a month.
IV. THE PROBLEMS AND POSSIBILITIES OF COMPARATIVE REACTION-TIME STUDIES.
Animal reaction time is at present a new field of research of evident importance and full of promise. A great deal of time and energy has been devoted to the investigation of various aspects of the time relations of human neural processes; a multitude of interesting facts have been discovered and a few laws established, but the results seem disproportionate to the amount of patient labor expended. Physiologists have determined the rate of transmission of the neural impulse for a few animals, and rough estimates of the time required for certain changes in the nervous system have been made, but this is all we have to represent comparative study. Just the path of approach which would seem most direct, in case of the time of neural changes, has been avoided. Something is known of the ontogenetic aspect of the subject, practically nothing of the phylogenetic; yet, in the study of function the comparative point of view is certainly as important as it is in the study of structure. In calling attention to the importance of the study of animal reaction time I would not detract from or minimize the significance of human investigations. They are all of value, but they need to be supplemented by comparative studies.