138 
must result in many invalids being deprived of 
a luscious and digestible food, and last, but not 
least, help to belittle science by reasoning 
which the common sense of centuries shows to 
be absurd. 
Contrast all this with the calm attitude of the 
scientific British Medical Journal, which contents 
itself, according to the quotation from it, with 
calling for scientific investigation of the reason 
for some beds being polluted.* It seems quite 
likely that isolated oyster beds might be con- 
taminated with bacilli, but the natural history 
of the oyster shows that he could not exist 
under such conditions, and that the bed would 
die out. In fact, the danger will apparently 
regulate itself. 
I hope that these remarks will draw the at- 
tention of practical biologists, competent to set 
the question at rest; at the same time they will 
serve to show the great need of at least an ele- 
mentary knowledge of science among our doc- 
tors before they presume to settle questions of 
the food supply of mankind; and they will 
serve to show the great lack of that knowledge 
among the rank and file of practitioners, who, 
at any rate, ‘out west,’ appear rather to glory 
in it. ; 
GEORGE CHAS. BUCHANAN. 
CEREBRAL LIGHT. 
In darkness or with closed eyes we can al- 
ways see irregular forms of light in our visual 
field. These forms are of various kinds, series 
of waves, successive rings that spread and break, 
ete. In addition to these definite figures there 
is always more or less definite irregular illumi- 
nation over the whole field. These phenomena 
are generally called the ‘retinal light’ or the 
‘ Higenlicht of the retina.’ They are usually 
supposed to arise from chemical changes going 
on in the retina. I wish to record some obser- 
vations that apparently prove them to be cere- 
bral and not retinal processes. 
1. With closed eyes there is only one illumi- 
nated field, not two, as there should be from the 
two retinas if the light were retinal. Two 
retinal figures might appear as one under the 
* Of. The investigations by Professor Conn, of Wes- 
leyan University, and of Professor Herdman, of Liv- 
erpool College. 
SCIENCE. 
[N.S. Vox. VI. No. 134. 
conditions: (a) Of suppression of one field, 
which is not the case here, because it is impos- 
sible to keep one field suppressed for many 
minutes, whereas I have watched the retinal 
figures in uninterrupted continuance for a long 
time ; (6) of perfect identity of form, which is 
hardly a possible supposition in the case of these 
irregular, volatile, chemical phenomena ; (c) of 
sufficiently similar construction for union by 
stereoscopic vision, which also is not the case, as 
there is no relief effect in the picture. 
2. The figures do not change in position when 
the eye is moved. They are localized in front 
and remain in the same place, even if the eyes 
are directed to one side. I find, however, that 
if the eyes are turned to a new position and 
kept there, the central figure (a spreading 
violet circle with a phosphorescent rim) will 
soon afterwards follow the movement ; there is 
thus a tendency for this figure to occupy the 
spot of sharpest vision. 
8. The figures do not change in location when 
the eyes are displaced. When the eyes are 
looking at some definite object, e. g., this page, 
a pressure of the finger on one of them will 
cause the page apparently to move. This is true 
whether the other eye is open or closed. Like- 
wise, if an after-image is obtained, it will move 
upon pressure of the eyeball. The pressure dis- 
places the eyeball and changes the projection of 
the retinal picture. This displacement does not 
occur with ‘retinal light.’ I have repeatedly 
observed these figures and have manipulated the 
eyeballs; I have found that they are not in the 
slightest degree affected by the manipulations. 
Tn order to avoid all possibility of errors of ob- 
servation, I have made the experiments in a 
series alternately with eyes open and eyes 
closed. With the eyes open I observed a dimly 
illuminated window; with them closed I saw 
the ‘retinal’ figures. The former always fol- 
lowed the displacements, the latter never. 
These observations are, I believe, sufficient to 
establish the proposition (which I have not seen 
elsewhere) that the phenomena of vision usually 
known as ‘retinal light’ and ‘retinal figures’ 
are not originated in the retina, but in the 
brain. They should therefore be termed ‘ cere- 
bral light’ and ‘ cerebral figures.’ 
The following hypothesis seems also justified : 
