Thermic hiftnences. 45 



normal when the low temperature of the part is corrected. Tem- 

 peratures below the freezing- point are, however, likely to so 

 disturb the vessel walls that inllammation of the tissue (swelling 

 and redness of the skin, frostbite, chilblain) develops with or 

 without the formation of blisters ; or after especially long and 

 severe exposure the blood and lymph circulation cease and the 

 tissue dies as a result. The necrotic area may be separated from 

 the normal by inflammatory reaction, or if it remain moist may 

 undergo putrefaction through the influence of invading bacteria. 

 The extremities are the parts of the body most commonly sub- 

 ject to freezing, but it is seen rather seldom among animals, for 

 example, the scrotum in bulls (Baiit:^), the paws in dogs, in 

 horses the thick skin of the hoof, particularly the crown and 

 pastern. Jewsejenko and Cadiot have recorded instances of 

 necrosis from freezing of the deeper part of the foot in horses 

 (in the Russo-Turkish and Franco-German wars, as well as in 

 Algeria). 



By the term catching cold (chilling) is meant the pathogenic 

 action of heat loss not sufficient to cause freezing, but produc- 

 tive of functional disturbances and inflammation of nerves, 

 muscles, joints and internal organs. The laity commonly and 

 primarily for almost all afifections attributes chilling as the cause ; 

 and even the physician often evades the question as to the origin 

 of some malady with the vague phrase of the possibility of catch- 

 ing cold, because of the obscurity of the aetiology of the case. 

 Many diseases formerly regarded as produced by exposure to 

 cold are now recognized in the advanced state of ^etiological in- 

 vestigation as infectious, although undoubtedly there is a group 

 of afifections in which chilling of large areas of the skin and 

 mucous membranes may with confidence be held responsible as 

 the causal agency. Such a relation is evident in cases where, after 

 unusual exposure to cold (thorough soaking, strong draughts, 

 falling into icy water, heat loss by radiation to some neighboring 

 cold object as a stone wall) there immediately develop in the 

 chilled parts pains, functional disturbances and symptoms of in- 

 flammation, or where in a short time these phenomena without 

 other demonstrable cause appear in the subjacent or more distant 

 parts of the body. Cats almost invariably become sick if they 

 become soaked by falling into the water, wdiile flocks of sheep 

 have been attacked by pleuro-pneumonia directly after wool 

 washing if, while wet, they were left exposed to cold air. The 



