274 H. S. LAWRENCE ET AL. 



Ciba Foundation Symposium (Lawrence, 1960b) and are sum- 

 marized in Table I. 



Transfer factor and skin homograft sensitivity 



The experimental design and the precise conditions ensuring 

 successful transfer of skin homograft sensitivity by means of 

 DNAse-treated leucocyte extracts obtained from the peripheral 

 blood of specifically sensitized humans have been set out in 

 considerable detail elsewhere (Lawrence et al, i960). For the 

 purposes of this discussion the basic experimental design followed 

 is: (i) Skin grafts from subject A were used to sensitize subject B. 

 (2) Leucocyte extracts containing anti-A transfer factor were 

 treated with DNx\se and injected into subject C. (3) Sensitivity 

 transferred to C was measured by the survival time of a test 

 graft from A compared to that of a control graft from D. (4) 

 A positive result was scored when the test graft was rejected in an 

 accelerated fashion (4-6 days) while the control graft was accorded 

 a first-set survival time (8-12 days). 



In the sensitization and testing procedures fuU-thickness, 

 II mm.-diameter skin grafts were used. The time of rejection 

 was determined by stereomicroscopic and gross criteria for 

 graft rejection described elsewhere (Converse and Rapaport, 

 1956). The appearance of rouleaux formation in the erythrocytes 

 coursing through the graft vessels, followed by thrombosis, 

 haemorrhage and extravasation of blood, heralded the downfall of 

 the graft. This was later reflected in the gross events of ecchymoses 

 and oedema which progressed to necrosis and eschar formation 

 of the grafted skin. 



The isolation, extraction and DNAse treatment of leucocytes 

 used for transfer of homograft sensitivity followed methods 

 previously described (Lawrence, 1955). The donors of skin and 

 leucocytes fulfilled the rigid criterion of not having transmitted 

 hepatitis following blood donations in the recent and remote past. 



