362 BIOLOGICAL EFFECTS OF RADIATION 



method of titration lacks accuracy, and his claim should not be accepted 

 until more convincing evidence is offered to counterbalance the more 

 extensive and more accurate determinations by Brooks, or to explain 

 the discrepancy. 



These experiments do not afford any ground for assuming that 

 colloidal processes or coagulation play a part in alexin photoinactivation, 

 but neither can they be regarded as evidence to the contrary. Processes 

 of this type may well go on to irreversible change very rapidly during 

 irradiation, not remaining in any unstabile wholly or partially denaturized 

 stage for any appreciable time. In this connection it is interesting that 

 Hassko (76) found the effect of irradiation upon the fluorescence of the 

 serum to be affected by the nature of the gases present more than was 

 the alexin activity. This fluorescence is one of the most sensitive indices 

 of change in proteins upon irradiation. 



A similar absence of any effect of irradiation was noted by Brooks (29) 

 in testing the inactivating effects of temporary acidulation. There was 

 no difference between control samples and irradiated samples which 

 were, therefore, not sensitized to low pH conditions. Nevertheless, this 

 experiment is suggestive in that inactivation occurs upon reaching a 

 pH (4.6 to 4.4) corresponding rather closely to the isoelectric point of 

 many globulins. 



Similar pH changes are involved in the so-called "fractionation" 

 of alexin into a mid-piece, or ''M piece," which is the globulin fraction 

 precipitated and redissolved, and an end- or "E piece," which is the residual 

 fluid containing albumens. This fractionation has been most successfully 

 done by Schubert (143), whose paper should be read by anyone interested. 

 His best preparations show E piece to have no hemolytic power, and 

 M piece to have very slight, if any, hemolytic power in salt solutions; 

 M piece dissolved in heat-inactivated serum becomes somewhat hemo- 

 lytic, and recombined with E piece regains practically all its hemolytic 

 power. Schubert regards M piece as the real alexin or lysin carrier. 



These M and E fractions have been the subject of endless experiment, 

 from which it seems probable that M piece is more sensitive to light than 

 E piece. Kagawa (95) seems to have established this fairly clearly for 

 ultra-violet light, and Koopman (100) has made similar observations. 

 Schubert (142) has made a still clearer demonstration because of his 

 better fractionation of alexin. His M piece retained less than 3 per cent 

 of its activity (upon recombination with E piece) when given an irradia- 

 tion which left the E piece totally unaffected (see also Kodama and 

 Shinomiya, 98a). 



These facts acquire increased significance when one notes that 

 according to Young (166) purified serum albumen is many times more 

 susceptible to coagulation by ultra-violet hght than the corresponding 

 globulin fraction. The former corresponds to E piece, which is Uttle 



