TUNEVALL AND LINDNER 



cause of differences in the choice of experimental animals and in- 

 fecting micro-organisms, and also of the mode of exposure to cold. 

 Thus, in one type of study animals have been exposed to cold under 

 conditions that provoke stress reactions, and chilling has generally 

 been found to increase the susceptibility. In 1878, Pasteur found that 

 chilled fowl became susceptible to anthrax. Increased susceptibility 

 to trypansomes at low environmental temperature has been seen in 

 guinea pigs (Kligler and Weitzmann, 1926); in rats (Kligler, 1927) 

 and mice (Kligler and Olitzki, 1931) to Bac, enteritidis; and in rab- 

 bits to streptococci (Carpano, 1926) and to syphillis (Longhin et al,, 

 1957), Other such experiments have shown lowered resistance of 

 chilled guinea pigs to pseudotuberculosis but not to pneumococci 

 (Burgers, 1929), indicating the importance of the choice of infecting 

 organism is important. This was also borne out by studies of 

 Previte and Berry (1962) in which chilled mice were abnormally 

 sensitive to relatively avirulent Salmonellae and staphylococci but 

 normally susceptible to virulent strains. It is noteworthy that 

 Bruneau and Heinbecker (1944) found that in dogs inoculated subcu- 

 taneous ly with /5- streptococci, cooling reduced the local inflam- 

 matory reaction and arrested bacterial growth. On removal from 

 the cold, however, both these processes were abnormally acceler- 

 ated, indicating that prolonged chilling had in the long run lowered 

 the resistance. 



In another type of experiment, body temperature has been lowered 

 in a way which avoids stress reactions. The results have been dif- 

 ferent in that infection with virulent Tj^De I pneumococci in rabbits 

 was not changed by hypothermia, whereas infection with normally 

 avirulent Type III pneumococci became lethal in hypothermic ani- 

 mals (Muchenheim et al,, 1943), Similar observations as to the re- 

 sult of infection with pneumococci of low virulence in rabbits were 

 made by Sanders et al, (1957), but they also found a decrease of the 

 survival time in virulent infection. On the contrary, Wotkyns et al., 

 (1958) working with mice found a longer survival time in hypother- 

 mc animals with Type III pneumococcal peritonitis suggesting de- 

 fense mechanisms. Similar observations on rats with peritonitis 

 were made by Balch et al, (19 55), and on rabbits with staphylococcal 

 sepsis by Grechishkin (1956), 



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