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Abstract Twenty‐four adult rats were given an injection of 3H‐thymidine at 4.00 p.m. and sacrificed two at a time everyhour for the next 12 hours. Another 24 adult rats were similarly treated but after inejction at 4.00 a.m. The brainswere fixed by immersion in Bouin fluid. Sections were stained with hematoxylin‐eosin and radioautographed. In another experiment two animals were sacrificed two and nine hours respectively after 3H‐thymidine injection and the brains were fixed in formalin. The sections were stained by silver impregnation and radioautographed. One hour after 3H‐thymidine injection, a number of glial nuclei were labeled: all were in intrphase. By 2–3 hours, labeled mitotic figures appeared and increased in number with time. From 4–5 hours after injection on, pairs of labeled nuclei were seen in increasing numbers. This sequence of events, which was observed with slight differences in the two main groups, indicated that labeled glia nuclei go through mitotic division. It is concluded that a low degree of mitotic activity continually takes place in the glial population of adult rats. About one fifth of the divisions seem to be in microglia. Most of the others seem to occur in cells of the oligodendrocyte family.
Hommes et al. (Wed,) studied this question.