ETIOLOGY OF DISEASE 127 



and local necrosis, followed by profound inflammation. 

 Burns involving large surfaces, one-third or more of 

 the body surface, often cause death, doubtless through 

 the production of poisonous products of tissue and blood 

 destruction. General high temperature leads to heat- 

 stroke, sunstroke, insulation, or heat exhaustion. In 

 these conditions there may occur hyperemia and edema 

 or even inflammation of the meninges, which lesions are 

 doubtless due to the production within the body of 

 poisonous substances the result of disturbed metabolic 

 processes. 



Cold. Exposure to extreme degrees of cold gives rise 

 to lesions similar to those produced by heat. Locally, 

 there are produced by excessive low temperature vesic- 

 ulation and necrosis, similar to burns. In exposure to 

 cold the extremities are first to suffer. The blood being 

 driven inward to maintain the internal bodily heat, 

 local anemia occurs, followed by vascular paralysis, 

 with hyperemia and necrosis. Prolonged exposure to 

 general low temperature leads to gradual obtunding of 

 sensibility and coma. 



Cold was formerly believed to be the cause of coryza, 

 pharyngitis, bronchitis, and similar conditions referred 

 to by the term "catching cold." It is now known to be 

 but a predisposing factor, the real cause being infection 

 with certain micro-organisms, the effect of cold doubt- 

 less being to lower the resistance and natural protective 

 properties of the body. 



