The mode of examination necessary when the hair has been blackened is different from that used when it has been decolorized. _The hair has been blackened._ As various methods of dyeing hair black are in use, the means of restoring the original color differ. The following are the methods most usually employed in dyeing: 1º. The hair is well rubbed with a pomade, in which finely pulverized charcoal is incorporated. This preparation, which is sold under the name of "_mélaïnocome_," possesses the disadvantage of soiling the fingers and clothing, even for several days after its application. 2º. The hair is moistened with a dilute solution of ammonia, and a perfectly neutral solution of a bismuth salt (chloride or nitrate) is then applied. It is subsequently washed, and allowed to remain in contact with a solution of sulphuretted hydrogen. 3º. The same operation is performed, a lead compound being substituted for the bismuth salt. 4º. A mixture of litharge, chalk, and slacked lime is applied, and the head covered with a warm cloth. The hair is afterwards washed, first with dilute vinegar, then with the yolk of an egg. 5º. The hair is first cleansed with the yolk of an egg, and then moistened with a solution of plumbate of lime; or, 6º. It is moistened with a solution of nitrate of silver, to which a quantity of ammonia sufficient to dissolve the precipitate first formed has been added. The first method merely causes a mechanical admixture of a coloring matter with the hair. In the four succeeding processes, a black metallic sulphide is produced; either by the subsequent application of a solution of sulphuretted hydrogen, or by the action of the sulphur normally present in the hair. In the last method, the formation of sulphide of silver doubtless occurs; but the principal change that takes place is probably due to the action of light, which, as is well known, decomposes the salts of silver. In order to restore the original color to hair which has been treated with "_mélaïnocome_," it is only necessary to dissolve in ether the fatty matters present, and then remove the charcoal by washing with water. In case the hair has been dyed by means of a bismuth or lead salt (as in methods 2, 3, 4 and 5), it is immersed for several hours in dilute hydrochloric acid: the metal present dissolves, as chloride, and the original color of the hair is rendered apparent. It then remains to detect the metal dissolved in the acid solution, in order to establish, beyond doubt, the fact that a dye has been employed. This is accomplished by means of the methods used for the detection of metals in cases of supposed poisoning.