386 J. F. A. p. MILLER 



4- to 5-week-old recipients by the method of Billingham and 

 Medawar (195 1). 



Adoptive imttiunization 



Normal 2-month-old C3H female mice were immunized 

 against normal Ak tissues, each mouse receiving bilateral skin 

 grafts and an intraperitoneal injection of cells from 2 thymuses and 

 2 spleens of i- to 2-month-old healthy Ak donors. Seven to 

 eight days later the mice were killed and cell suspensions were 

 prepared from their axillary and inguinal lymph nodes and 

 spleen. From 20 to 50 milUon such cells were injected intra- 

 peritoneally into appropriate recipient mice. 



Blood counts 



Differential and absolute white cell counts were performed on 

 tail vein blood at 6 weeks of age. 



Histology 



Sections were fixed in Bouin's fluid and in bufferered neutral 

 formalin. They were stained routinely with haematoxylin and 

 eosin and where necessary with Unna-Pappenheim stain. 



Results 

 Weight curves and mortality 



The body weights of mice thymectomized and sham-thy- 

 mectomized at birth were recorded at intervals during the first 

 three weeks of life and are shown in Fig. i. It can be seen that 

 there is no significant difference between the two groups. 



Mortality in the thymectomized group was high after two 

 months of age, as many as fifty per cent of the mice in some 

 strains dying from a syndrome which, clinically, closely resembled 

 the runting syndrome. Tliis was characterized by progressive 



