DEFENSIVE MECHANISM IN RELATION TO INFECTION 103 



demonstrated experimentally that the daily administration, to rabbits, 

 of 5 to 10 c.c. of alcohol introduced into the stomach by a tube, renders 

 these animals more susceptible to infection with Streptococcus pyogenes - 

 and Bacillus coli. Wagner, Leo, and Platania have also found animals 

 that under the influence of chloral, phloridzin, alcohol, and curare are 

 more susceptible to infection. 



(/) Exposure to cold and wet frequently lowers the resistance of 

 man and other warm-blooded animals to infection. The influence of 

 these factors, well illustrated in the etiology of "colds" and pneumonia, 

 is not without experimental foundation. Thus Pasteur found that 

 fowls, which are naturally immune to anthrax, are readily infected if 

 they are inoculated after their body temperature has been reduced by 

 a cold bath. Conversely, Gibier 1 has shown that frogs, which are also 

 naturally immune to anthrax, are readily infected if their temperature 

 is previously elevated and maintained at 37 C. 



(g) Trauma and morbid conditions in general may predispose to in- 

 fection. Thus injuries reduce the local resistance and facilitate local 

 infections that vary with the severity and extent of the trauma. The 

 increased susceptibility of injured joints and pneumonic lungs to tuber- 

 culosis; the frequent and oftentimes extensive streptococcus infection 

 accompanying scarlet fever and smallpox; the increased susceptibility 

 of diabetics to furunculosis and local gangrenous lesions of the skin 

 all show the increased susceptibility of individuals already injured or 

 diseased to infection. 



THE DEFENSIVE MECHANISM OF THE MICROORGANISM IN RELATION 



TO INFECTION 



After bacterial invasion has occurred, the question of whether or 

 not the microorganism can overcome the defensive forces of the host and 

 prove pathogenic may depend to some extent upon the peculiar defensive 

 factors of the invading bacteria against the offensive mechanism of the 

 host, aside from their toxins or other distinctly offensive forces. 



Morphologic and Physiologic Changes of the Microorganisms. For 

 example, capsule formation or thickening of the ectoplasm of certain 

 bacteria is evidence of their increased powers of resistance against the 

 opposing forces of the host. The capsule may be quickly lost when the 

 microorganism is cultivated on artificial media, and its virulence be cor- 

 respondingly lowered, but by repeated animal inoculations a race of 



1 Compt. rend. Acad. de Sci. de Paris, 1882, xcix, 1605. 



