to the sample and from the average energy of the electrons. This technique is usable only when there are ample amounts (gram quantities) of material available so that the entire electron beam may be stopped in the sample itself. Pollard and co-workers (3) have irradiated enzymes by allowing an electron beam to pass entirely through the sample; however, their apparatus does not permit the collection of irradiation products, and they have not attempted to estimate the total energies absorbed by their samples. In recent work at this laboratory, we have been carrying out the electron irradiations of 50- to 100-mg samples of crystalline choline analogs contained in glass tubes under high vacuum. In these irradiations the entire electron beam was allowed to pass through the sample and to impinge on an electron collector mounted behind the sample holder. The sample holder and the electron collector were mounted in a high vacuum so as to avoid air-scattering of the electron beam and air ionization. Finally, the effect of secondary electron emission on the