26 S. G. ANDERSON 



a. Ultraviolet Irradiation. Ultraviolet light first destroyed the infectivity of 

 PR8 strain of influenza in dialyzed allantoic fluid. Then the following pro- 

 perties were destroyed, in order — toxicity, ability to interfere, ability to 

 immunize, ability to elute, hemagglutinin and complement-fixing antigens, 

 probably 600 S before 30 S (Henle and Henle, 1947). 



b. Aging. Hemagglutinin in allantoic fluid retained its full titer at 4°C. for 

 several months (Miller and Stanley, 1944). Because of the frequent deposition 

 of urates from untreated allantoic fluid, it is more convenient to dilute the 

 fluid with saline before storage. 



c. Heating. Myxovirus strains show wide variation in the temperature at 

 which hemagglutinin is destroyed. Burnet (1951a), for instance, has reported 

 two substrains of WS (influenza A 1933) which have thermal inactivation 

 points of 67 (WSM) and 52°C. (NWS), respectively, when exposed for 30 

 minutes. Hanson et al. (1949) observed a similar wide range in susceptibility 

 to thermal inactivation in a collection of Newcastle disease virus strains; 

 some were inactivated at 56°C. in 5 minutes, others required up to 6 hours. 



The eluting power of a virus is frequently destroyed by a degree of heating 

 which leaves the hemagglutinin intact. This gives rise to so-called "indicator" 

 virus (Stone, 1949b). For some strains, conversion to the indicator state 

 occurs only if heating is carried out under special conditions, e.g., at pH 8.5 

 in the presence of citrate in the case of MEL virus. 



d. Hydrogen Ion Concentration. At 23 and 4°C, the hemagglutinin of 

 PR8 was best preserved at pH 7 in phosphate buffer, swine virus at pH 7 to 

 8, and LEE at pH greater than 9 (Miller, 1944). PR8 hemagglutinin was 

 stable for 30 minutes throughout the range of pH 2.4 to 10.3 (Hirst, 1948a). 

 Other factors concerned in the stability of hemagglutinin at different hydro- 

 gen ion concentrations were the concentration of virus, and the presence of 

 other proteins, amino acids, such as arginine and glycine, and salts. 



e. Periodate Ion. Potassium periodate, at an appropriate dilution and in 

 the relative proportion of 8 mg. or more per milliliter of allantoic fluid, 

 acting on LEE virus, destroyed the hemagglutinin (Fazekas de St. Groth 

 and Graham, 1949). Below this concentration hemagglutinin remained, but 

 at concentrations of 1 mg. per milliliter or greater, virus enzyme was damaged 

 and virus would not elute. These results were virtually independent of the 

 final molarity of the periodate. 



/. Trypsin. Trypsin did not destroy hemagglutinin, but in high concentra- 

 tion it reduced the enzymatic activity, producing an indicator virus from 

 LEE (Hoyle, 1952; Stone, 1949a). 



g. Formaldehyde. Added to allantoic fluid in final concentration of 0.1 to 

 1.0 %, formaldehyde destroyed the hemagglutinins of PR8 and LEE over a 

 period of several days at 4°C. (Hirst, 1942b; Chu, 1948d). Mumps hemag- 

 glutinin was reduced in titer by 0.04 % formaldehyde after 24 hours at 



