Reticulocytes and their Humoral Regulation.

The reticulocytes are generally accepted to be young red blood cells. Whenever red cell formation in the bone marrow is active the proportion of reticulocytes in the blood increases; hence the importance ofthe reticulocyte count in haematology. Nevertheless, there have been few studies dealing with purely physiological and chemical aspects. A study of the ripening of reticulocytes into mature non-reticulated red cells has, however, been carried out in our laboratory during the last five or six years. The present article reviews the results obtained. Experimental Procedure Rabbits were used as experimental animals. In order to obtain reasonable accuracy in counting their reticulocytes, the animals were brought into a chronic anaemic state by the daily withdrawal of from 30 to 50 ml. ofblood. At the end ofone week the haemoglobin percentage thus fell to 40 or 50 and the red cell count to 2 or 3 million per c.mm. of /4, blood, with 20 or 30 per cent reticulocytes. a_ This state could be maintained for a month or more before the animals died. /2 The blood of such animals was used in the tests (Plum, 1942a). Blood was centrifuged and the red cells /O washed in saline. They were then resuspended in saline, or in plasma or saline to which had been added the substance whose action on the reticulocytes was to be studied. The suspensions were kept in 6 small test-tubes in a water bath at 40° C. __ and gently and constantly moved. Samples 6 for reticulocyte counts were taken at x regular intervals. Reticulocytes suspended in saline alone X 4 disappeared slowly, but the rate of disk appearance could be accelerated considere ably by adding commercial liver extract to 2 the saline in which the cells were suspended (Fig. 1). The youngest and most unripe types of reticulocytes disappeared first, and as there was apparently no haemolysis 0