PROCEEDINGS AM. PHILOs. Soc. VOL. LI. No. 204

PLATE I

Normal Rabbit: Cerebrum.

Frightened Rabbit: Cerebrum. The rabbit was frightened once and immediately killed. Note the hyperchromatism.

Frightened Rabbit: Cerebrum. The rabbit was frightened once and killed at the end of six hours. The cells are more swollen than in the normal.

FEAR IN RABBITS.

These and the following cuts are intended to show that fear and exophthalmic goitre cause demonstrable morphologic changes in the nerve cells of different parts of the brain which vary in degree [rather than in specificity] according to the part of the brain.

The rabbits used in the fear experiments were frightened by dogs without being injured or without making muscular efforts of any consequence.

Normal rabbit:

PROCEEDINGS AM. PHILOS. Soc. VOL. LI. No. 204

PLATE II

Cerebellum. The average of ten differential Purkinje cell counts from ten rabbits was: Active cells, 64.8 per cent.; fatigued cells, 34.5 per cent.; exhausted cells, 0.7 per cent. [For comparison with cuts on Plate III.]

Frightened rabbit: Cerebellum. The rabbit was frightened once and killed immediately. The average of ten differential Purkinje cell counts from ten such experiments was: Active cells, 83.4 per cent.; fatigued cells 15.7 per cent.; exhausted cells, 0.9 per

Frightened rabbit: Cerebellum. The rabbit was frightened once and killed at the end of two and one half hours. The average of five differential Purkinje cell counts from five such experiments was: Active cells, 55.6 per cent.; fatigued cells, 35.4 per cent.; exhausted cells, 9.0 per cent.

FEAR IN RABBITS.

These cuts and the cell counts as given above illustrate several important points, viz., that cerebral stimulation by fear causes, first, demonstrable morphologic changes in brain cells, second, a marked early increase in the number of active [and hence also hyperchromatic] cells, and, third, that this stimulation is followed by later and more serious morphologic changes in the cells which do not attain a maximum until from 2% to 6 hours have elapsed after the period of fright.