69 
therefore be situated much higher than 300—600 M.C.S. Now it 
results from the above table that if the back receives about 1400 
M.C.S., negative curvatures may occur. In this neighbourhood there- 
fore the maximum of the growth retardation curve must lie; there 
may be considerable individual variation; if the maximum lies some- 
what higher, a feeble positive reaction will still be possible; if it 
is at or below 1400 M.C.S., negative curvatures can occur, this 
depends on the degree of slope of the descending portion. We can 
also calculate from table IT that a negative curvature never occurs, 
if the back receives less than 1400 M.C.S. Thus 1756 M.C.S. on 
the front and 1006 M.C.S. on the back still give a strong positive 
curvature; here the y of 1756 M.C.S. must be greater than the y 
of 1006 M.C.S. We may therefore place the maximum of the growth 
retardation curve at about 1400 M.C.S. 
With a unilateral illumination the posterior side will not be 
maximally retarded until the anterior receives m < 1400 M.C.S. 
This amount of energy must of course lie beyond the threshold value 
for the negative curvature, for otherwise y, could never become 
larger than y, and no negative curvature could occur. From this the 
value of m can be found approximately. 
I shall indicate yet a third method by which the course of the 
growth retardation curve can be explored. This can be done by 
assuming the magnitude of the maximal curvature to be 
proportional to the difference between the front and back growth 
retardation. If the maximal strengths of curvature are then plotted 
against the energy values as abscissae, there results a curve of 
the differences of growth retardation between the anterior and 
posterior sides. By a simple mathematical calculation, the growth 
retardation curve of the front can be calculated from the curve of 
differences, whereby it is assumed again, that the back receives + 
of the energy of the front; here the magnitudes of the growth 
retardation do not of course represent absolute values. The points 
of the posterior growth retardations are found by subtracting the 
curve of differences from the anterior curve; these can also be 
found by plotting the anterior curve with abscissae four times as 
great (rule of products). The magnitudes of the maximal curvatures 
I have deduced from tables 1 and 3 of Arisz; the energy was here 
always applied in 10 sees. Since the front is exposed to the full 
energy’), we have here again plotted the course of the growth 
retardation curve. In this way we come to the following result: 
1) See footnote p. 61. 
