The rate of metaphase accumulation in the bone marrow cells of AKR mice treated with colchicine was investigated. The influence of this alkaloid on the differential count of the bone marrow cells in these animals was also studied. It was demonstrated that the stathmokinetic effect of colchicine on the bone marrow cells started almost immediately after the administration of the drug. The number of arrested metaphases increased linearly from one-half hour to six hours after the injection of colchicine, and then fell rapidly.

In rats injected with colchicine, the changes in the bone marrow concentration of this compound were followed for eight hours. The colchicine concentrations increased from the first to the fourth hour, and then fell rapidly, reaching the zero level at the eighth hour.

From the results obtained, it appeared that four hours post-injection was the most convenient time for the study of the bone marrow proliferative activity by the colchicine method when 1.2 mg./Kg. of colchicine per body weight was used. The fact that four hours after the injection, a mild decrease in the percentage of mature bone marrow granulocytes was found, may represent a limiting factor, which is, however, of moderate importance in the application of this technic.

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