Beginning with the work of Hodge numerous researches have been made on the histological and micro-chemical changes in ganglion cells in diiferent states of physiological activity.Both the changes observed as w-ell as their interpretation are in many respects a t variance; which may, in part, he due to the different methods employed, but probably also to the fact that the states of rest, activity and fatigue of the cell as typified by change in structure and chemical reaction are probably separated by imperceptible gradations only.As electrical stimuli were in many cases resorted to bring about the conditions of activity and fatigue of the cells.Nissls in 1896 pointed out the invalidity oP, without further proof, identifying the changes observed in the cells on such treatment as identical with the changes that may accompany normal physiological functioning.The vertebrate retina seems to offer the best field where conditions of rest, activity and fatigue may without much difficulty be induced by variations in the normal physiological stimulus.The first investigator to study the finer structural difference6 in the cells of the stimulated or fatigued and of the resting retina was Mann (1894).'H e did not confine his observations to the retina, but 'This work was begun in the fall of 1900 a t the suggestion of Prof. F. M. McFarland.It was intended to extend the observations t o the retinae of reptiles and ashes, b u t a s other work has intervened the note is recorded in i t s present form.
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A. J. Carlson (1903) studied this question.