DISCUSSION 87 



enhance to the soHd form now, so that it seems that at least some 

 quantitative differences between these two forms of the same tumour 

 have developed. 



Eichwald: I have a question regarding the assay system in which you 

 use the promotion of tumour growth. You express your results as the 

 number dying out of 10 mice. If a mouse dies before the end of your 

 critical period how do you count that in your final fraction of 10 mice ? 

 This may seem rather petty, but since the groups are fairly small, a 

 difference of one or two mice may make a great deal of difference. 



Kandutsch: In these particular experiments no mice died from causes 

 other than the growth of the tumour. However, sometimes it happens 

 that one mouse dies from some unknown cause before the period when 

 the tumour would kill them, although this tumour kills in about two 

 weeks, or three at the most. In this case I have usually expressed it as a 

 percentage, even though it seems a httle extreme when you have only 

 10 mice. 



Feldman: I was very interested in your application of snake venom to 

 this antigenic preparation, so that you are able to change the physical 

 properties of your material without apparently changing the antigenic 

 behaviour. I believe snake venom has a high content of lecithinase. 

 Did you try to see whether there is lecithinase activity in your snake 

 venom preparations, and whether its action could explain your results ? 



Kandutsch: At least one procedure for isolating lecithinase from snake 

 venom has been reported, but the venom used is from a tropical 

 rattlesnake rather than the Eastern diamond-back, which is the one I 

 had. When I tried to apply that procedure to my snake venom I 

 obtained a fraction but it did not produce the effect I had observed with 

 whole venom. I haven't yet really examined this to see whether it has 

 in fact lecithinase activity. Snake venom has, besides lecithinase activity, 

 several proteolytic enzymes, diphosphoesterases and perhaps many 

 more. 



Davies: There is undoubtedly lecithin in the lipid fraction of my 

 material. Lysolecithin is the product produced by snake venoms from 

 lecithin, and when I add lysolecithin to my material it also clarifies the 

 solution, but with loss of activity. 



Kandutsch: My material, once it has been digested with the snake 

 venom, undoubtedly still has a fairly large lipid portion attached to the 



