WALKER 



only within certain limits of temperature. For many strains a tem- 

 perature of 40° C or above inhibits multiplication and viral pro- 

 duction is depressed below 33° C. It appears that elevated tempera- 

 ture produces a block in the second half of the virus multiplication 

 cycle and low temperatures block the first part of the cycle. But he 

 points out (also Dubes and Wenner, 1957) that strains vary in the 

 temperature that is optimum for their multiplication and that, in 

 general, neuro virulence in monkeys is associated with those strains 

 that are capable of good multiplication at 40° C, and lack of viru- 

 lence with those incapable of multiplication at 37° C or above. 



There is additional evidence from quite a number of studies using 

 tissue cultures or chicken embryos (Enders and Pearson, 1941; 

 Thompson and Coates, 1942; Sharpe, 19 58; Hoggan and Roizman, 

 1959; Wheeler and Canby, 1959) that the temperature range within 

 which viruses can multiply vigorously is often quite limited, and 

 that the upper limit in particular may be quite sharp and abrupt. 

 For several of the viruses studied the optimum temperature for 

 multiplication is a degree or two below that of the internal body 

 temperature of some of the common mammalian hosts, I want to men- 

 tion briefly some data concerned with mumps virus, because it 

 could conceivably provide some insight into how cold could affect 

 latent infections, 



Hinze and I have been studying a carrier system of mumps virus 

 in human conjunctiva cells. This system has been maintained for 

 several years (Walker and Hinze, in press). The cells multiply at a 

 rate comparable to control cultures, and show little evidence of 

 deleterious effect even though use of fluorescent antibody demon- 

 strates that 90 per cent or more of the cells contain viral antigen. 

 As routine, these cultures are grown at 37° C, at which tempera- 

 ture about 1 of every 100 cells appears to be excreting virus as 

 judged by the fact that erythrocytes will adsorb to the cell surface. 

 There is a low level of virus in the medium. At 37° C practically all 

 of the cells contain antigen, but it is restricted to a few sharply out- 

 lined, discrete, massesinthecytoplasm(Fig. 8a). At 40° C the anti- 

 gen is perhaps even more restricted in its distribution (Fig. 8b). 

 But at 35° C or 33° C the antigen becomes widely distributed in the 

 cytoplasm in small granules (Fig. 8cand8d) and the cells tend to be- 

 come rounded and ragged in appearance. At 35° C or 33° C erythro- 



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