DAMACxE IN AEROBIC AKD ANAEROBIC SYSTEMS 29 



the volume of material to be irradiated. Suspensions of bacteria have 

 been exposed to 30 krad (Dewey and Boag, 1059, 1960) and volumes 

 of solution suitable for spectrosco])ic analysis have been exposed to 

 over 100 krad in a single pulse (J. W. Boag and 11. E. Steele, un|)uh- 

 lished). For spectrosco[)ic analysis a light-source has been developed 

 (Boag, 1957), the output from which during a flash of a few micro- 

 seconds' duration, enables absorption spectra to be recorded at medium 

 dispersion. Such records show the reagents present at a given time after 

 a 2 fjLsec exposure to ionizing i^adiation. By means of a photomultiplier, 

 set to record at the absorption peak of a known reagent, the rate of 

 appearance or disappearance of that reagent may be recorded as illus- 

 trated in Figs. 2 and 3. 



These flgures show certain aspects of the oxidation of a 10~3M FeS04 

 solution in the presence of OSN H2SO4 and in the presence or absence 

 of NaCl. It will be seeii that the absorption band at 305 m/x character- 

 istic of the ferric ion makes its appearance 20 times more slowly than 

 the absorption (as yet unidentified) at 240 m/x. The values of the times 

 required for half the final optical density to appear are 1200 /xsec and 

 60/xsec respectively for the two wavelengths. It is evidently quite 

 feasible to carry out kinetic studies for species which occur in the visible 

 and u.v. for lifetimes of this oi'der, or even considerably smaller, with 

 this type of equipment. 



The apphcation of similar methods to cell suspensions is, of course, 

 very much more difficult on account of non-specific light scattering, 

 but the methods developed by Britton Chance (1952) and others are, 

 in principle, applicable. ESR spectroscopy is likely to prove more 

 widely applicable than light spectroscopy to the study of radical 

 kinetics in cells which have been exposed to ionizing radiation. In order 

 to take advantage of the high dose-rate during the pulse, Dr. Boag is 

 constructing in our Laboratory a spectrometer in which the magnet has 

 an axial hole through which the electrons may enter the resonant 

 cavity. It is hoped that this will make radicals of lifetimes greater than 

 100 jLisec open to investigation. 



In general, the relatively slow process of diffusion across the cell 

 envelope limits the speed with which the chemical composition of the 

 intracellular fluid may be changed. In certain respects, oxygen is 

 exceptional, since it is consumed in radiochemical reactions (cf. next 

 section). 



Loss of reproductive integrity by the bacillus Serratia marcescens 



Several aspects of the loss of reproductive integrity by Serratia marces- 

 cens have been studied by my colleague, Dr. D. L. Dewey. In all the 



