~6<
Acthal raonse may either directly or indirectly incrcase the rate of utilization.
Por example, ¢he animals become susceptible to infection, and the development of
infections will definitely ineczcase ¢he rate of utilication.
Thus the rates of
utizication that are mcasured in an irradiated animal may at times give valucs
3
that ase greater than the normal utidication,
In the case of piatelets, this
doses not secn to be the case.
8.5
Sensitivity Factor.
Taere is considerable difference in the radiosensitivity of the stem
cells.
recursoss of erythrocytes (Dicom and Bloom) and lymphocytes (\iarrcn) are
extremely sensitive to joaicing scdiction.
The precursors of the granulocytic
serics ase apparently less radiosensitive.
Megataryecytes appear relatively une
diminished in nunber in the bone marrow of dors exposed to Lethal amounts of
rodiation for a period of 3 to 4 days after irradiation.
In fact, mesasaryocytes
are still seen on the third day in the bone mesrow of docs exposed to 3009 r of
2.0 mev total body xeray, an aexsunt of radiction that is about seven tines the:
hundred pes cent icthal dose for dogs.
In general, the immature and proliferating
bicod cells are more sensitive to irsadiation than the adult biood celis.
However,
tne reticuloencothelist celi, the comzen ancestor for all biocod cells, is remarke
ably radioresistant.
In other words, radiosensitivity of the blood-forming coll
seems to co throush a masimun in the course of maturation (fig. 1).
Under normal
conditions, the actively prolifcratinz cclls are the more radiosensitive.
Last statement anparentiy does not hold for 241 conditions,
This
Investigations by
Jacobson et ai. have shown that emtrcmely hyperplastic erythroid tissue is markedly
radiocesistant.
In addition, Tuiiis has presented histologic evidence that there
axe exceptions to the iaw of Bergonié ond Tribondeau.
resistance of the reticulcendothelict
It seems that the radio-
cell and of hyperplastic erythroid tissus
Cf
chaiilenses in part the classical law of Beegenié and Tribondeau.
This law states,