Aniline stains resembling blood are changed to greenish-yellow or yellow on the addition of dilute nitric acid. Eosin stains produce a fluorescent solution when dissolved in water. Grease, tar, pitch, snuff, and paint may be mistaken for blood, especially on dark fabrics. They may be detected by two methods: (_a_) =The Wet Method.=--Having failed to obtain a solution by the aid of the ordinary solvents for blood, other solvents must be used; ether or benzene for grease, paint, or tar. The solution obtained must be examined with the spectroscope. (_b_) =The Dry Method.=--Place the cloth or other fabric stain down upon a clean white filter paper; then on pressing the cloth with a hot laundry iron, grease, tar, or pitch will stain the paper, paint or snuff will not. CHAPTER VII BURNS AND SCALDS, CONTUSIONS AND BRUISES BURNS AND SCALDS Burns and Scalds are lesions characterised by a more or less marked destruction of the tissues of the body, caused by the action upon its internal or external surfaces of a temperature higher than that of the body itself, or by the action of corrosive chemical substances. =Burns= are produced in the following ways: By exposure to radiant heat. By the direct application of flame. By contact with heated solids. By contact with solid bodies which have become liquefied by heat, such as metals in a state of fusion. By friction. By lightning, electricity, and X-rays. By contact with corrosive chemical substances, solid or liquid. =Scalds= are produced by the application of heated liquids, at or near their boiling-points, or in a gaseous form--as _steam_. The injuries produced will depend upon the degree of temperature, the period of exposure to its action, and the extent of surface involved. The danger to life depends more on the extent of surface injured than the intensity of the burn or scald upon a limited area, unless the position of the burn render it peculiarly dangerous. Even though the injuries be comparatively superficial, if they involve one-third or one half of the surface of the body they must be regarded as fatal. They may prove fatal by shock, by asphyxia, by constant and profuse discharge from the injured surface, from absorption of septic matter, from secondary inflammations of internal organs and serous membranes--pleurisy, peritonitis, meningitis, perforating ulcer of the duodenum. Children succumb more quickly than adults to burns and scalds--the simplest, in their case, often proving fatal. The cause of early death from burns and scalds is looked upon as a disorder of the blood following injury to the red corpuscles by the heat, and that this is more easily brought about in children, because of the thinness of the skin, and the red corpuscles being less capable of resistance. The following table gives the different degrees of burns: