Vie CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. II

RECIPRCCITY LAW FAILURE FOR LIGHT SENSITIVITY
OF BULL SPERMATOZOA
C. VAN DUIJN Jr., and J.H. van LIEROP
Biophysics Dept., Research Institute for Animal
Husbandry "Schoonoord", Zeist, The Netherlands.

When cells are irradiated the energy dose D is
proportional with the product of the intensity I and the
time of exposure t. According to Bunsen & Roscoe's (1)
reciprocity law of aequivalence of I and t in a photo-
chemical process it is expected that the biological
effect should be linearly proportional with the dose
D=I.t.

However, this simple aequivalence of I and t holds
only in the case of one-quantum processes. These are
characterized by a truly exponential relationship
between dose and effect and independence of temperature.

In studies on the effect of illumination on spermato-
zoa of bull (4) and cock (3) light sensitivity was found
to vary with temperature. A definite darkness effect,
consisting of a higher rate of deterioration in dark-
ness after a period of illumination as compared to
controls having been kedt in darkness all the time, has
been demonstrated, too (6). Further, in investigations
of our own sigmoid survival curves have been observed
at very high intensities. In view of these observations
deviations from the reciprocity law are to be expected.

METHODS. Five series of experiments have been perform-
ed with 20 ejaculates from 6 bulls of FH and MRY breeds.
Semen was diluted with ultra-microscopically clear

egg-yolk - citrate medium (7). Split samples were
placed in a calibrated step wedge, consisting of 11
compartnents with identical series of Ilford gray
filter screens at both sides. At both sides one
fluorescent tube (Philips 40W/33) was mounted. The
intensity range was 0 - 116Q0 lux. The temperature was
kept constant at 7.4 + 0.1 "C.

At each intensity measurements of numbers_of normally
moving spermatozoa N, their mean velocities v and
migration rates N.V were performed with Rikmenspoel's
photo-electric method (8), at equal intervals of 110 min
over a total period of 8 h. During illumination the
test tubes with semen were in a horizontal position
with a rather shallow layer of liquid in order to
prevent disturbing effects of settling. Prior to sampl-
ing for measurement they were put upright and mixed
1gain. Conditions were completely aerobic.

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