962 THE ANIMAL VIRUSES 



hand, if dried slowly at room temperature, and kept at room temperature over 

 H2SO4, it survived for 3 to 6 months. Noguchi (1918) found that, when dried, 

 vaccinia virus remained alive for over a year, but its virulence was considerably 

 decreased. Haagen (1939), on the other hand, observed no loss of virulence in 

 a year when mouse brain infected with vaccinia was dried over calcium chloride 

 and kept in sealed glass vessels in the ice-chest. One hour's exposure, to the 

 August sun, of the foot-and-mouth virus, dried on a glass slide, inactivated it. 

 Most viruses appear to be very resistant to cold. Vaccinia virus withstands a 

 temperature of — 180° C. for months, and even repeated freezing and thawing 

 fails to destroy it. Frozen and dried, they may live for months (Sawyer et al. 1929, 

 Wooley 1939). Vaccinia virus in dry powdered form withstands dry heat at 

 100° C. for 5 to 10 minutes. Moist heat at 55-60° C. for half to one hour is fatal 

 to most viruses, but blood from swine fever is said to withstand a temperature 

 of 58° C. for at least 2 hours ; it is inactivated, however, within an hour by a 

 temperature of 78° C. Some viruses, like the poliomyelitis virus, are rapidly 

 killed by ultra-violet light. Many are also susceptible to photodynamic action 

 (see Chapter 5), and succumb in a few minutes when exposed to a concentration 

 of about 1/100,000 methylene blue in the presence of daylight (Perdrau and Todd 

 1933, Herzberg 1933, Shortt and Brooks 1934). Alpha rays, X-rays, and gamma 

 rays are all lethal (Lea and Salaman 1942). 



Most viruses exhibit a fairly high resistance to glycerol, and one of the best 

 methods of preserving infectious tissue is to suspend it in 50 per cent, glycerolated 

 saline, cover it with liquid paraffin, and store it in the ice-chest (Perdrau 1927). 

 Pure glycerol destroys the viruses fairly rapidly as a rule ; thus Noguchi (1918) 

 found that vaccinia virus was destroyed by pure glycerol at 4° C. within 24 hours, 

 though in 40 per cent, glycerol it survived for about 6 months. The preservative 

 action of glycerol probably depends on the inhibition it exerts on autolysis of 

 the infected tissue (Rivers 1928). 



Survival in distilled water, saline, or Ringer's solution, varies considerably. 

 In the ice-chest many viruses will survive for a long time, but most of them perish 

 rapidly if kept at room temperature or 37° C. The foot-and-mouth virus in saline 

 rarely survives at 37° C. for more than 24 hours ; and the lymphocytic chorio- 

 meningitis virus is non-infective within 3 hours at 20° C. (Lepine et nl. 1937). 

 Susceptibility to oxidation may be chiefly responsible for this behaviour. At 

 low temperatures the presence of tissue cells seems to be beneficial to the survival 

 of viruses, but at higher temperatures the reverse is probably true. Amies (1934), 

 for example, found that vaccinia virus remained virulent much longer at 37° C. 

 when stored in the form of a suspension of elementary bodies than in tissue culture. 

 In general, the presence of serum or 0-5 per cent, agar is beneficial for survival, 

 as is also storage under anaerobic conditions (Zinsser and Tang 1929, Zinsser and 

 Seastone 1930, McClean and Eagles 1931). The optimum H-ion conceiitration 

 for survival of the foot-and-mouth virus and the vaccinia virus is pH 7-6 ; between 

 pH 4-0 and 3-0. vaccinia virus is rendered non-infective within about an hour 

 (Beard et al 1938). 



Disinfectants. — Vaccinia virus in testicular suspension is said to survive in 

 0-5 and 1-0 per cent, phenol solutions for over a year at 4° C, but to be destroyed 

 by 2 per cent, phenol within 24 hours, and by a 1/30,000 solution of iodine within 

 1 hour at 37° C. (Noguchi 1918). Likewise, ectromelia virus in a suspension of 

 mouse's liver will remain virulent in 0-5 per cent, phenolized saline at 4° C. for 



