A technique for the daily examination of spleen colonies in mice

We have developed a surgical method and an insertable device for viewing the daily changes in number, shape, and development of hemopoietic spleen colonies in mice. With it we have been able to follow the spleen colony changes in individual animals over the period when macroscopic or moderately magnified counts of spleen colonies are customarily made. We have found that about half of the spleen colonies present on day 8 after transplantation do remain through day 12, while an approximately equal number disappear during this period. Further, the colonies that disappear are replaced by an equal or larger number of newly developing colonies at roughly the same temporal sequence as their disappearance. We speculate that these late-appearing colonies may be late arrivals from the recipient's previously seeded bone marrow.