OBSERVATIONS ON THE EFFECT OF SPLEEN-SHIELDING 



to routine laboratory methods to determine the number of nucleated cells 

 per mm^. Since the suspensions taken from individual mice varied from 

 a maximum of 10 X 10^ cells in 0-5 cm^ of diluent to a minimum of 0-07 X 10^ 

 cells in 0-5 cm^ diluent, pooled marrow aspirations were made and the 

 suspensions were standardized so that 0-5 cm^ contained the number of cells* 

 we wished to administer intravenously to each irradiated mouse. The total 

 number of nucleated cells injected per mouse used in these studies varied 

 from 39-0 X 10« to 0-13 x 10". 



Although survival was found to be enhanced with as few as 0-5 X 10" 

 cells per mouse, a suspension that provided each mouse with 5 to 10 X 10" 

 cells proved to be the most effective (54-9 per cent survival) in decreasing 

 mortality [Table I). With a suspension of 1 to 5-0 X 10" cells per mouse, 

 33-3 per cent of the animals survived the 28-day period of observation. As 

 the number of cells was decreased, the per cent survival decreased corre- 

 spondingly ; only 11-6 per cent survived when less than 1 X 10" cells were 

 given to each mouse, and none survived when less than 250,000 cells were 

 injected. It must be emphasized that suspensions containing more than 

 10 X 10" cells in 0-5 cm^ were no more effective in enhancing survival than 

 those containing 1 to 5 X 10" cells. Of 196 mice that received more 

 than 10 X 10" cells, 81 or 41 per cent survived the 28-day period of observa- 

 tion. The incapacity of these concentrations to provide the protection afforded 

 by lesser amounts is being studied. 



The results described above were obtained with marrow from adult 

 (10- to 12-week) mice. When young mice (4- to 6-week) were used as 

 donors, the results were more gratifying since fewer cells were necessary to 

 obtain comparable results. There was 78-7 per cent survival when 7 to 

 8 X 10" cells were given {Table II). Studies are now in progress in which 

 mice that had been irradiated with lethal amounts of X-rays were given less 

 than 3x10" cells and as few as 50,000 nucleated cells. The data suggest 

 that survival is effectively enhanced even when the total number of nucleated 

 cells falls below 1 X 10". 



Effect of spleen-cell injections on survival of irradiated mice 



Studies of the effect of cells from the spleen on the survival of irradiated mice 

 were also carried out in a way that was similar to that described for the bone 

 marrow suspensions. In the original experiments, the spleen cells were 

 obtained by inflating the extirpated mouse spleen with saline or Locke's 

 solution. The cells that were thus extruded were injected intravenously 

 into mice that had been subjected to 900 r. 



In later experiments, the spleens from adult mice were mashed gently in 

 a mortar, or cut and pushed through a syringe, and suspended in Locke's 

 solution. All of the cells that could be removed conveniently with a 26-gauge 

 needle were used to make the suspension. In some instances, the cells were 

 centrifuged and washed several times with Locke's solution before the final 

 suspension was made. Since the spleens from baby mice are very fragile, it 

 is necessary only to push them through a syringe to release the cells desired 

 for injection, and centrifugation is not necessary. 



* Cells refers throughout the paper to the nucleated cells counted in an acetic acid (2 per 

 cent) dilution. 



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