DISCUSSION 213 



Medawar: Did not Wigzell try this ? 



G. Klein : He tried, but I don't think his results are consistent enough 

 to be able to attribute splenomegaly to humoral antibodies. 



Eichwald: You had very large numbers of animals per group. This 

 implies of course that there were several litters per group. How much 

 variation in spleen size was there from litter to litter within the same 

 group ? 



Simonsen: In my Table I, I showed this as a standard error for each 

 dose level. There is quite a variation from one litter to another in the 

 sensitivity to a given dose but nevertheless when you pool the data from 

 several litters you get a very nice dose-response curve. Of course the 

 variation in sensitivity from one htter to the other would affect the 

 immune cells and the normal cells equally, which makes the variation 

 between the litters rather irrelevant. 



Eichwald: A related question: to what extent is it permissible to divide 

 up the Htter and mark members of the Htter by a surgical or cheirdcal 

 method, either painting them red or green or cutting off the left toe 

 or the right ear, and thereby setting various nutritional or infectious 

 hazards ? The mother may not like the altered infant and therefore 

 it does not get a good nipple and as a result you have a small mouse. 



Voisin: It should not affect the weight of the spleen. 



Simonsen: The mothers always cheerfully accept these marked 

 animals; and I have no indication that it affects the health of the 

 mice. There are always negative controls, that is to say animals injected 

 with isologous cells, and they don't runt or show other peculiarities 

 compared to non-injected controls. 



Medawar: Of course one could randomize the marking system and 

 thus eliminate that source of error, and at the same time make it quite 

 impossible to interpret one's results ! 



Michie: If you don't randomize the marking system, you will, in 

 course of time, fmd a systematic and spurious difference between two 

 animals in the same litter which ought to show no difference, so that if 

 cutting off a tail has an effect, it will show up. 



Brent: J. B. Solomon reckons that there is some sex effect when pro- 

 ducing splenic enlargement in chickens, the degree of enlargement 

 depending on the sex of the donor and the recipient. Does this enter 

 into your graft-versus-host assay ? 



TRANS. — 8 



