Frost-bite is caused by cold depressing the vitality of a part or the whole of the body. The frost-bitten part is at first blue and puffy, from the current of blood through it being much retarded; then, should the cold be continued, it becomes pallid, and the painful tingling gives place to numbness and insensibility, and finally to actual death or mortification, with a dark livid appearance of the part. Although a sudden violent application of cold may cause death of the tissues, by reducing the temperature to a degree incompatible with animal life, the most common cause of the destructive effects of frost-bite is undoubtedly the excessive reaction which occurs on sudden removal of the cold, or the application of heat; this is especially the case with moist cold.
Baron Larrey believed that 'cold was merely the predisposing cause of frost-bite, and mentions that after the battle of Eylau the French soldiers did not experience any painful sensations during the severe cold varying from to below zero of Réaumur's thermometer; but, when the temperature rose from to , they felt the first sensations of cold, and applied for succour, complaining of acute pains in their feet, and of numbness, heaviness, and prickings in the extremities. The parts were scarcely swollen, and of a dull red colour. In some cases, a slight redness was perceptible about the roots of the toes, and on the back of the foot; in others, the toes were destitute of motion, sensibility, and warmth, being already black, and, as it were, dried.' Those of the men who indulged in the warmth of the bivouac fires suffered from frost-bite in much larger proportion than their more hardy comrades. But 'the extent of disaster from this cause even in modern campaigning may be judged from the fact that in the French army before Sebastopol 2800 cases occurred in two nights, and of this number 900 subsequently died.'
In Great Britain cases of frost-bite are comparatively rare. Occasionally, in severe winters, cases present themselves at the hospitals in the persons of houseless, ill-nourished unfortunates, whose constitutions have in many instances been enfeebled by spirit-drinking.
The treatment of frost-bite consists in coaxing back by degrees the vitality of the part; this is most prudently effected by rubbing the part in a cold room, at first with snow, then with water at ordinary temperature, and when warmth returns by enveloping it in cotton-wool or flannel without applying heat. As the coldness subsides, the painful tingling returns, then redness and heat; in a short time the latter will be above the natural standard, and, if the reaction is severe, the part will inflamm, and perhaps mortify. It is well to remember that the part need not have been actually frozen for these symptoms to occur. The person with languid circulation who, coming home with cold wet feet, places them before the fire, or in warm water, may be 'frost-bitten' to all intents and purposes.