KASHA: Why did you exclude metastable states in the case of other mole- 

 cules ? 



PLATZMAN: I did not mean to infer that there are not any. But there is at 

 least one case which has been studied in which the concentration of the impurity 

 necessary to discharge the excited atom is much greater, indicating a shorter 

 lifetime for the latter. However, this part of the work has been only little de- 

 veloped. 



BURTON: In organic molecules there would probably be some very low- 

 lying metastable states, but they would not give ionization. 



KASHA: That is the point. In fact, we will discuss this after Dr. Linschitz's talk. 

 Metastable states are more readily excited in larger molecules than in rare gase 

 atoms, butas Dr. Burton indicates, the energy would be insufficient for ionization. 



PLATZMAN: Mercury has a comparatively low ionization potential, and, 

 since mercury is a very common impurity, the implications of its possible pres- 

 ence should be one of the grains of salt added to the interpretation of all older 

 measurements of W. 



That is all I had planned to say, and although we do not have very much 

 time for discussion, I hope that Dr. Pollard and Dr. Fano will contribute re- 

 marks -- and also, of course, anyone else who wishes to do so. 



POLLARD: The remarks that I have to make might perhaps fit in a little 

 better this afternoon, if you are going to discuss the actual length of tracks of 

 low energy electrons then. But what I wanted to point out was that we have a 

 line of low voltage work in which the voltage of the electrons varies from zero 

 to 5000, and we use these for bombarding bacterial spores, bacterial virus, 

 and viruses in general, and making measurements on the surface area as 

 measured by the loss of infectivity of the material and also loss of the serolog- 

 ical combining power. 



In the course of this it became very necessary to know the range of elec- 

 trons in the kind of material we were working with and, as you point out, the 

 theory is very poor down there. This is where the Born approximation doesn't 

 hold too well. So we looked for a way by which we could make a sure measure- 

 ment of the range of low voltage electrons in biological material. What we did 

 was to take essentially a very thick enzyme layer on a plate, to be precise, 

 and simply burn off with a complete bombardment as much of the enzymes as 

 the particular energy would take. That is to say, the experiment consists of 

 putting down a layer of enzyme, known in amount by the way in which it is 

 pipetted there. Then you expose it to long-time bombardment of electrons of 

 different energies. Then you assay it. If very low voltage electrons are used 

 you get a rather interesting result. A monomolecular layer of invertase is 

 inactivated. As you increase the energy of the electron this same picture 

 continues until you pass through the molecule, and this occurs with an energy 

 of about 150 electron volts. Thereafter you start to go up and you should go 

 up in steps, but the steps get blotted out and the result is one can get an esti- 

 mate of the thickness of the material traversed from about 300 to about Z000 

 electron volts. This lies a little lower than Lea's theoretical curve. But it 

 follows it quite well, and this represents, therefore, experimental data on the 

 way in which energy is lost. 



FANO: This is the practical range, so it is bound to be lower than Lea's 

 figure which was meant to be the true range. 



