SESSION IV DISCUSSION
897
the feed. Originally, we thought it was due to availability, or what we
called availability (and I suppose it reallyis);i.e., the cesium in natural
feeds was less available to the animal, and, as I pointed out rather
briefly tn the talk, we do find large differences between high-concentrate, or high-grain, rations and those which contain predominantly
hay or forage. We feel that cesium in forage is less available and in
grain is more so. The cesium chloride isotope solution should be even
more available.
Our work, the little we have done, seems to indicate it is a matter
more of adsorption in the digestive tract, the undigested fibrous material adsorbs cesium and carries it out in the feces. This seems to
agree fairly well with the observations of Patrick and others at Oak
Ridge some years ago in working with rabbits and rats where they
found that, if they fed the animals fibrous feed, a much higher percentage of the material was excreted in the feces. It also agrees with
the well-established fact that there is a higher percentage excreted in
the feces and a smaller percentage in the urine of ruminants as compared to nonruminants. The major difference between the species is
that ruminants depend on a highly fibrous feed.
LENGEMANN: What would the radiocesium content of the milk be
if the milk cows were consuming a high grain diet?
WARD: The figure I gave, 0.3% per liter, referred to a diet con-
taining about 20 lb of hay and 10 lb of grain, which is about the average
diet for milk cows in the United States. When we fed the minimum of
hay, about 5 lb, and 20 to 30 lb of grain, the figures were 0.6 to 0.7%
per liter. If one wanted'to feed astraight grain ration, which introduces
a lot of complications, the percentage presumably would go somewhat
higher.
VAN MIDDLESWORTH: Dr. Ward, if the adsorption in the gut is
partly responsible for this cesium loss, could your data suggest that
added carrier cesium in the diet would increase the absorption rather
than decrease it?
That is, saturating the adsorption capacity with
carrier perhaps would cause an increased absorption of fallout material rather than a decreased absorption. The body burden would be
increased by giving carrier. Such a result is the opposite of the usual
and expected result of addition of carriers.
WARD: I suppose that is right. I think, in the case of the "Cs, we
are talking about such small numbers of atoms of material that if it
were saturated this could well be the case.
LENGEMANN: Mr. Rivera, in some of your calculations, you used
0.35 for the discrimination factor for the infant from zero to one year
of age. On the basis of the data reported by Dr. Beninson, it is difficult
to see how such a value could arise.