154 



Discussion 



produced antibodies against the rat bone marrow. We have no explana- 

 tion for the next 25 per cent. They lose weight, some go down to 9 g. 

 and then die. 



Van Bekkum: I'm very glad that Dr. Loutit has been able to demon- 

 strate so admirably that his original point of view with regard to the 

 mechanism of bone marrow therapy is the correct one. I should like to 

 mention some of our results in this field which are in essential agree- 

 ment with Dr. Loutit's findings. The point is that we have employed 

 quite different techniques to identify the origin of the haematopoietic 

 cells in mice which survived a lethal dose of total body irradiation as a 

 result of homologous or heterologous bone marrow injections. These 

 experiments were carried out in collaboration with Dr. O. Vos, Mr. 

 J. A. G. Davids and Mr. W. W. H. Weyzen. The methods are summar- 

 ized in Table I. The first technique is based on the observation that 



Table I (Van Bekkum) 

 Evidence for the Cellular Hypothesis 



Combination 



Homologous 



Heterologous 

 Heterologous 



Surviving mice, 

 identification of 



Bone marrow 



Erythrocytes 

 Granulocytes 



Method 



Therapeutic effect 

 in irradiated donor 

 and receptor strain 



Specific antisera 



Histochemical 



isologous bone marrow cells are about 20 times more effective than 

 homologous bone marrow cells when injected into lethally irradiated 

 CBA mice (Fig. 1). In other words, you need about 20 times more 



^t SUHVIVALS 

 AT JO DAYS 



too' 



90- 

 80- 

 70- 

 60" 



50' 



40- 



30- 



20- 



10- 



10' 



• o o- 



•o c- 



• t 



o. 



I ' "I 



TT 



10» 



"T 1 1 I I I I 11 



I I I I ■ I mniBSR OP CELLS 



■n 



10' 



10' 



10" 



Fig. 1. (Van Bekkum). Therapeutic effect of i.v. bone marrow cells in 



irradiated mice. 

 O Isologous. Homologous. A Heterologous (rat). 



