Vol. 6, 1920 
PSYCHOLOGY: A. C. HARDY 
221 
it should be noted that in this material there is no further formation of 
rods. The coarsely granular precipitate is well marked in the second and 
third divisions, but no rods are formed. 
It is evident that my conclusion from a study of the material described 
is that the basophilic bodies found are not in the nature of chromidia, but 
are the result of indirect nuclear activity. As to the applicability of these 
results to cases in which basophilic inclusions occur normally, it is impossi- 
ble to say more than that such cases should be considered in the light of 
the evidence here given. The explanation offered for the formation of 
the basophilic extra nuclear bodies described is intended to be suggestive 
rather than conclusive. It brings together facts which have not hitherto 
been associated. 
A more detailed paper with illustratons is forthcoming. 
Beckwith, Cora J., The Genesis of the plasma-structure in the egg of Hydractinia 
echinata, /. Morph., 25, 1914. 
Chambers, Robert, Microdissection Studies I, Amer. J. Physiol., 43, 1917; and Micro- 
dissection Studies II, /. Exper. ZooL, 23, 1917. 
DantchakofT, Vera, Studies in cell division and cell differentiation I, /. Morph., 27, 
1916. 
Gatenby, J. Bronte, The Cytoplasmic Inclusions of the Germ Cells, Part V, Quar. 
Jour. Mic. Set., 63, 1919. 
Schaxel, Julius, Das Zusammenwirken der Zellbestandteile bei Eireifung, Furchung, 
und ersten Organbilung der Kchinodermen, Arch. Micr. Anat., 76, 1911; Plasmastruc- 
turen, Chondriosomen und Chromidien, Anat. Anz., 39, 1911. 
Wilson, E. B., Archoplasm, Centrosome, and Chromatin in the Sea-Urchin Egg, J- 
Morph., 1 1 , 1895. 
A STUDY OF THE PERSISTENCE OF VISION 
By Arthur C. Hardy 
Department of Physics, Massachusetts Institute of Technology 
Communicated by Edwin B. Wilson, February 20, 1920 
Introduction. — It was observed by Allen/ while investigating the effect 
of the color of the light on the persistence of vision, that there seemed 
to be portions of the retina where the persistence of the retinal impres- 
sion was less than on the fovea. That is, when no flickering of the color 
under observation was perceptible in the center of the retina, a slight 
movement of the eye in any direction which allowed the light to fall upon 
the peripheral portions of the retina was sufficient to destroy the apparent 
continuity of the light. Allen attempted to measure the persistence for 
regions on the temperal side of the retina at 10 and 20 degrees from 
the axis of the eye but found that the results were "too uncertain to be of 
any use." The writer has measured the persistence of vision for several 
colors within the cone whose semi- vertical angle is nearly 40 degrees. 
More than one hundred points on the retina within this area were observed 
for each color used. From these data, it is possible to construct a map 
of the retina showing the persistence of v^ision for each portion. 
