246 HILDEMANN, LINSCOTT AND MORLINO 



cell inoculum died of acute runt disease was at first difficult to 

 reconcile with the well-defined immunogenetic system employed. 

 However, a scrutiny of the technical variables involved pointed to 

 inadequate cell dosage as a probable factor. This could be attri- 

 buted to (i) failure to remix the cell preparation frequently, vdth 

 consequent settling of cells during the course of injections, and (2) 

 occasional leakage of a small drop of the inoculum from the heart 

 puncture after withdrawal of the needle. From this standpoint, 

 the median survival times calculated on the supposition of trun- 

 cated distributions are less valid than those based on death of all 

 animals receiving 900,000 or more lymphocytes. Nevertheless, 

 the same quahtative conclusions may be drav^oi on either basis. 



Evaluation of lymphocyte-induced transplantation disease 

 by the weight-gain and organ-enlargement assays 



All animals employed in this investigation were maintained 

 under standardized conditions recommended for optimum 

 growth and development (Byerly, 1957). Neonatal mice from 

 many htters were individually weighed from the 5th to the 48th 

 day of age. Weight-gain curves were then determined for normal 

 A/Jax mice and for A/Jax mice that received 0-9-1 -5 million 

 C57BL/6 small lymphocytes via the heart during the day of 

 birth. For the most part, the normal mice were httermates of the 

 injected mice. Mean weights with their standard errors are 

 plotted in Fig. 3 for 64 normal mice and for 107 experimental 

 mice, representing a total of 433 and 542 individual weights, 

 respectively. The curve best fitted to the normal weight-gain 

 values reveals a sigmoid distribution that levels off after 30 days 

 and rises rapidly again after 40 days. The levelling is probably a 

 consequence of weaning at 30 days and adjustment to sohd food. 

 A significant curtailment of mean weight increase reflecting runt 

 disease in experimental animals was evident at nine days, which 

 was also the day the first death occurred. From this time until 

 about 30 days, the disparity in weight gain between experimental 



