SECONDARY BACTERIAL INFECTION IN MICE 



hypothermia. Halpern et al. (1951) studied the activity of the RES, as 

 judged by its ability to clear colloidal carbon, in hypothermic rats 

 and found a decided reduction in function. In rats at normal tempera- 

 tures, 90 per cent of the carbon was "fixed" in the RES in 35 min- 

 utes, while in the hypothermic animal 29 per cent was sequestered. 



Frohlich (1938), in studies of wandering phagocytes, found an in- 

 crease in number of polymorphonuclear leucocytes in hypothermic 

 rabbits, as noted by others, but up to 65 per cent of the cells were 

 either injured or were atypical. Similarly, Taylor and Dyrenforth 

 (1938) reported an impairment of phagocytic activity of fixed tissue 

 cells in human subjects immersed in water at 20. 3° C. It was 

 claimed, moreover, that low environmental temperatures predis- 

 posed to infections, especially in the upper respiratory region, but 

 the evidence was not convincing, primarily on the basis of sample 

 size. A decrease in blood content of complement and opsonin was 

 found by Wildfuhr (1950) in persons exposed to cold. Thus, the 

 humoral as well as the cellular defense is said to be altered by cold. 

 In some host-parasite systems, therefore, low ambient temperatures 

 are generally deleterious and seem to enhance not only an infection 

 already underway but seem to "unmask" any secondary involvement. 



Attempts to compare data obtained from various laboratories 

 suffer, unfortunately, from the lack of adequate standardization in 

 experimental design. That different host- parasite models are used 

 assumes little importance in face of the realization that not all in- 

 vestigators report the duration of the photo period per day and the 

 housing conditions employed. Furthermore, the term "cold", de- 

 pending on the investigator, frequently spans sizeable temperature 

 ranges. Even the conditions used in the studies just described are 

 quite artificial and may not have a counterpart in nature. Animals 

 were subjected to a constant and unfluctuating cold. This forces them 

 to live at a level ofhigh energy expenditure for long periods, a con- 

 dition seldom known to occur with any certainty in nature. Moreover, 

 the photo period was always 12 hours of light per day, and the light 

 intensity was constant. This, too, of course, is contrary to the 

 natural state. In spite of these apparent shortcomings, the results 

 were constant and reproducible. Evidence for a decreased host 

 resistance in the cold to infection with S. typhimur ium is convincing 

 and is even easier to accept in view of the increased incidence of 



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