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changes which in some may cause the lowered re- 

 sistance which is so often referred to as a condition 

 for infection. Exposure to cold has long been 

 known as an important predisposing factor, al- 

 though we continue in ignorance of its precise 

 effects. Animals are more susceptible to pneumo- 

 coccus infection after artificial reduction of the 

 body temperature. It is possible that a lowered 

 body temperature may decrease antibacterial ac- 

 tivities; that the activity of the bactericidal fer- 

 ments of the plasma or of the leucocytes may be 

 suppressed, or phagocytosis may be inhibited so 

 that organisms which reach the bronchi and peri- 

 bronchial lymphatic structures are allowed to pro- 

 liferate. It is probable that in health the leuco- 

 cytes continuously pass through the bronchial and 

 alveolar walls where they may englobe foreign par- 

 ticles (coal dust) or bacteria, and leucocytes are 

 present on the mucous membranes of the mouth 

 cavity. Following exposure and the reduction of 

 the body temperature, or following the prolonged 

 inspiration of cold air, the activity of the phago- 

 cytes may be inhibited so that cocci which reach 

 these surfaces are not ingested and continue to 

 proliferate, or the same conditions may decrease 

 the exudation of the leucocytes from the vessels. 

 It is possible also that the activity of the ciliated 

 epithelium is reduced similarly so that the cocci 

 are not so readily carried to the exterior. 

 other Extreme exposure is not always followed by 

 pneumonia, however, and not all cases of pneumo- 

 nia are preceded by exposure; many other condi- 

 tions may predispose to infection, as a lowered 

 resistance due to alcoholism, other infections or to 

 non-infectious processes. That certain local con- 



