276 H. S. LAWRENCE ET AL. 



sensitize donor blood leucocytes to the degree that is necessary for 

 systemic transfer, this exposure to antigen is sufficient to effect a 

 local transfer of sensitivity. It is known from earlier experience 

 with transfer of delayed sensitivity to bacterial antigens that 

 juxtaposition of antigen and transfer factor increases the intensity 

 of the transfer and allows for a tenfold reduction in dosage of 

 leucocytes (Lawrence, 1949). 



It was also concluded that even in this more sensitive transfer 

 system, a positive non-specific effect of non-sensitive leucocyte 

 extracts could not be detected; nor did a specific effect of sensitized 

 donor serum reveal itself. 



(2) Systemic transfer: in this technique of transfer the DNAse- 

 treated leucocyte extract obtained from a sensitized donor is 

 injected into the shoulder of the non-sensitive recipient. Eight 

 days later test and control grafts are applied to the recipient's 

 forearm. When this technique is used both grafts become vas- 

 cularized by the third day of residence. Twenty-four hours after 

 vascularization (on the fourth day) the test graft had undergone 

 the haemorrhage and thrombosis of accelerated rejection while 

 the control graft was accorded a first-set reaction of rejection 

 (e.g. recipient No. 11: test graft survival, 4 days, control graft 

 survival, 11 days; recipient No. 24: test graft survival, 4 days, 

 control graft survival, 13 days). 



From this group of experiments it was concluded that although 

 a first-set and second-set exposure to skin grafts was not sufficient 

 to sensitize donor leucocytes to the degree necessary to effect a 

 systemic transfer, a sequential series of four sets of skin grafts 

 applied to the same donor was a sufficient sensitizing antigenic 

 stimulus to allow systemic transfer. 



Systemic transfer however will not occur when the donor 

 of leucocyte extract is sensitized by four sequentially apphed 

 grafts if each homograft after the first undergoes a ''white 

 graft" reaction rather than the usual accelerated reaction of 

 rejection. 



