364 PAUL S. RUSSELL 



injection of sensitized cells at 5 days of life was particularly bene- 

 ficial appears in Fig. 11. The variation in effectiveness of this late 

 cell treatment appears to occur largely between Utters rather than 



S4 



o 

 m 



5 DAY 

 Cell Reeciuipment 



DBA sens 

 cells l/V 



2 4 6 8 10 12 



16 20 24 

 DAYS of AGE 



Fig. 1 1 . Individual weight-gain records of a litter of 6 

 newborn C57BL/6 mice all of which received an intra- 

 venous injection of 12 million DBA/i spleen cells at 

 birth. On the fifth day of life four animals (solid dots) 

 received a second intravenous injection of 18 million 

 spleen cells from adult C57BL/6 mice which had pre- 

 viously rejected skin grafts from DBA/i donors. This 

 is a particularly favourable example of the protective 

 effect which can be achieved by a relatively late injection 

 of sensitized cells. 



within a single litter and may be attributable in part to differences 

 in the immunological capacity of the cells used in different experi- 

 ments. Microscopic examination of the spleens and lymph nodes 

 of surviving animals treated in this way at about 4 weeks of age 

 reveals considerable hyperplasia with many active germinal centres 



