DISCUSSION 
in children and disappears when they become adult. Children 
are not fertile, and we wondered whether the thymus gland has 
a hand in this. From the thymus glands of calves we were able 
to isolate, partially, a substance which increases growth in 
young animals and also sterilizes animals, both males and 
females equally. We then found that the growth-promoting 
substance and the sterilizing factor are different; we have been 
able to separate them chemically. If the “sterilizing factor”’ is 
administered to an adult mouse it has no after-effect. If it is 
given to very young mice, then it makes the animals sterile for 
life; the sexual organs do not develop. Unfortunately we have 
not yet been able to produce the substance in crystals or in 
great quantity, but I hope that very soon we will be able to do 
so. All that I can say about it now is that it is not a steroid, 
since it contains nitrogen. I would like to collaborate with Dr. 
Pincus in studying this compound further. 
Pincus: I read a preliminary account of this finding with 
great interest. Have you any idea on which phase of repro- 
duction this factor is active? 
Szent-Gyérgyi: We have no idea yet. We only know that if 
we give this substance to either the male or the female two 
days before copulation, then no progeny will be produced. 
Wolstenholme: It has been suggested that anti-ovulation 
drugs, by allowing follicles to remain unruptured in the ovary, 
would prolong the period of life during which women could 
ovulate and therefore presumably become pregnant. Assuming 
that there were no unpleasant side-effects still to come and that 
these drugs were taken almost continuously by women except 
when they wished to be pregnant, there might be a chance 
that women of 60 and 70 would have no menopausal symptoms 
and might be ‘“‘marriageable”’ up to a much later period. Is 
there any validity in this argument? 
Pincus: The initial crop of eggs with which each female is 
supplied declines regularly with advancing age and so far all 
experimental studies which have attempted to alter the rate of 
disappearance of the odcytes (which are the young eggs, so to 
speak)—except by using X-rays—have failed. 
108 
