84 KADIATION MIOLOGY 



iiovoUy rather than its commercial importance. Emmons and FIol- 

 laender (1939) showed that the curve which represents the efficiency of 

 different wa\(> lenf!;ths of ultraviolet producing mutations in fungi par- 

 allels closely the germicidal-action curve. Hollaendcr and l^mmons 

 (1941, 194()) correlated mutants of fungi produced by ultraviolet irradia- 

 tion with the naturally occurring species probably produced by sunlight. 

 From this, techni(iues have been developed for obtaining mutants, for 

 example, for better yields of citric and itaconic acids and of penicillin 

 and the similar antibiotics (see chapters on bacteria and fungi). 



PROTECTION AND PROCESSING OF PRODUCTS 



Because of its high germicidal effectiveness compared with its other 

 photochemical, erythemal, and thermal effects, ultraviolet energy, espe- 

 cially of wave length 2537 A, has been used for the protection and disin- 

 fection of many products of so unstable a composition as to prohibit the 

 use of more conventional methods. Such applications have developed 

 in food, pharmaceutical, and beverage processing and storage places. 



MOLD, ANTIBIOTICS, AND PARENTERAL FLUIDS 



The mold-derived antibiotics and many parenteral li(}uids are very 

 susceptible to contamination by the normal mold and bacterial content of 

 air. This contamination is often of a chemical nature precluding terminal 

 sterilization by heat. Some serums and antitoxins are developed by the 

 growth of bacteria and viruses which must be finally inactivated by 

 methods which will not at the same time destroy the desirable properties 

 of the preparation. Ultraviolet has served to protect such materials 

 during processing and to provide a final inactivation where controlled 

 bacterial growth has been a part of the process. The germicidal lamps 

 are used in ducts and hoods, over work tables, for upper-air disinfection, 

 and also for thin-film irradiation (Fig. 2-18) l)y the methods previously' 

 discussed. 



BLOOD PLASMA 



One of the more unusual applications of ultraviolet is for the dis- 

 infection of blood plasma of the hepatitis virus. Several commercial 

 devices have been developed. All provide for irradiation in films of the 

 order of }/ioi)o in- in thickness or for the violent agitation of somewhat 

 thicker films. It is important to remember that, because of the low 

 penetration of the ultraviolet, changes in film thickness, even of micro- 

 scopic dimensions, may seriously interfere with any of these methods. 

 These methods and devices have already been discussed generally for 

 absorptive liquids (Figs. 2-16 and 18). Preliminary to the use of any 



