SEASONAL CHANGES IN RETICULOCYTE NUMBER AND IN RELATIVE WEIGHTS OF THE SPLEEN, THYMUS, AND KIDNEYS IN THE NORTHERN RED-BACKED MOUSE

Abstract

Seasonal variations were observed in reticulocyte numbers and relative organ masses of the spleen, thymus, and kidneys in the northern red-backed mouse, Clethrionomys rutilus, in the vicinity of College, Alaska, during 1963 and 1964. There was a significant correlation between reticulocyte level and relative spleen weight and between relative spleen and thymus weights. There was no correlation between reticulocyte number and relative weight of the paired kidneys, but there were corresponding peaks in these parameters which appeared to be approximately 1 month out of phase with increase in kidney weights preceding increases in reticulocyte numbers. The probable significance of these variations is discussed in terms of adjustments of the red-backed mouse to seasonal cold exposure.