MODIFICATION OF RUNT DISEASE 355 



Storage. Where test skin grafts were performed they were done 

 in the manner referred to above. 



Weights 



The weight of each neonatal animal was measured to the nearest 

 o- 01 g. on the first or second day of life and generally every two 

 to three days thereafter throughout the period of the experiment. 



Histology 



Microscopic examination of tissues has been confined to 

 standard preparations made after fixation in lo per cent formalin 

 or Zenker's formol, by paraffin embedding, sectioning at S[i and 

 staining with alum haematoxylin and eosin. 



Results 



I. Runt disease, general features 



(i) Time course of development and pathology. Normal neonatal 

 C57BL/6 mice begin life with a period of rapid gain in total 

 body weight which is fairly linear over the first 30 days (Fig. i^). 

 Although this curve of normal growth is reliable enough to be 

 used as a background for comparison of gross changes, controls 

 within a single litter have been used whenever possible. Follow- 

 ing the intravenous administration of 5 to 10 million DBA/i 

 spleen cells, newborn C57BL/6 mice follow a normal course of 

 weight gain until the sixth or seventh day. At this time (see 

 Fig. i^) there is a sudden cessation of weight gain. The animals 

 enter upon a "plateau period" and soon thereafter begin to die. 

 Of 140 neonatal recipients receiving about 5 to 15 milhon 

 foreign spleen cells intravenously on the first day of life all but 

 <^ (3 ■ 7 per cent) died of the effects. The median age at death was 

 14 days (Fig. 2). Three of these survivors were later grafted with 

 DBA skin which was fully rejected by 11 days indicating no 



