There was at that time in Rome a celebrated mistress of the art of poisoning, named Locusta. She was in prison, having been condemned to death for her crimes. Though condemned she had been kept back from execution by the influence of Agrippina, on account of the skill which she possessed in her art, and which Agrippina thought it possible that she might have occasion at some time to make use of. This Locusta she now determined to consult. She accordingly went to her, and asked her if she did not know of any poison which would immediately take effect upon the brain and mind, so as to incapacitate the patient at once from all mental action, while yet it should be gradual and slow in its operations on the vital functions of the body. Locusta answered in the affirmative. Such characters were always prepared to furnish any species of medicaments that their customers might call for. She compounded a potion which she said possessed the properties which Agrippina required, and Agrippina, receiving it from her hands, went away. Agrippina then went to Halotus, the servant who waited upon the emperor and gave him his food,--and contrived some means to induce him to administer the dose. Halotus was the emperor's "taster," as it was termed:--that is, it was his duty to taste first, himself, every article of food or drink which he offered to his master, for the express purpose of making it sure that nothing was poisoned. It is obvious, however, that many ways might be devised for evading such a precaution as this, and Halotus and Agrippina arranged it, that the poison, in this case, should be put upon a dish of mushrooms, and served to the emperor at his supper. The taster was to avoid, by means of some dextrous management, the taking of any portion of the fatal ingredients himself. The plan thus arranged was put into execution. The emperor ate the mushrooms, and Agrippina tremblingly awaited the result.