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

subjected the DNA of both fresh and aged spermatozoa to but one
trypsin digestion during isolation and then he has used this remain-
ing washed DNA-protein material as an antigen in serological studies.
The DNA-protein material from the fresh spermatozoa contained only
one serologically identifiable antigen. The DNA-protein from the
chromatin of aged bovine spermatozoa contained two separate ard dis-
tinct serological types. |s then a change in the protein of chroma-
tin on spermatozoan aging the key to the aging phenomena of male
gametes? Experiments are in progress to verify and further test
this observation.

Other important questions concerning the generalizations which
can be drawn from these investigations come to mind. For example,
is the male gamete of the bovine, the rabbit, or the frog a really
good cell in which to determine the pacemaker alterations in the
fundamental chemistry of biological aging? If one can generalize
from results with spermatozoa which are mature and nondividing for
tissues in which the cells grow and divide, then aging per se involves
opportunities for damage to the genetic information transfer system
of cells. These opportunities may occur with far greater frequency
outside of the metazoan body than they do in it, but this question
has not really been tested by experiment.

Summar

This is a review of the recent work from I11inois involving
1,014,925 inseminations of cattle in which semen was stored for 5
days at 4°C, for several months to one year at -79 to -88°C (in
mechanical storage),and for several months up to two yearsat-|96%.
Fertile bull semen improves in fertility for a time after collection,
reaches on optimum,and then declines in fertility as the spermatozoa
age. Embryonic loss follows an inverse of the fertility. The opti-
mum fertility and the minimum of embryonic mortality for storage at
4°C occur on the day after collection, they occur under our condi-
tions from the second to the fourth month of storage at -79 to -88°C
and from the fourth to the eleventh month of storage at -196°C. On
further storage fertility declines and the proportion of embryo
development failures increases. The early improvement in fertility
is believed to be due to selective death of spermatozoa containing
aberrant chromatin during early storage. After the period of opti-
mum storage, the decrease in fertility and the increase in early
embryonic death found is due to a degradation in the integrity of
the genetic information system. The adenine-thymine and cytosine-
guanine base ratio of the spermatozoan DNA does not change during
aging, though there is a continuing turnover of C'4 in the DNA even
at -196°C storage. However,aging of frog spermatozoa causes changes
in DNA which decrease the productionof RNA in frog embryos produced
by them and results in fewer proteins being synthesized by the em-
bryo.

197