Lucretia, Volume VI by Edward Bulwer-lytton

The reader will doubtless have observed the consummate art with which the poisoner had hitherto advanced upon her prey. The design conceived from afar, and executed with elaborate stealth, defied every chance of detection against which the ingenuity of practised villany could guard. Grant even that the deadly drugs should betray the nature of the death they inflicted, that by some unconjectured secret in the science of chemistry the presence of those vegetable compounds which had hitherto baffled every known and positive test in the posthumous examination of the most experienced surgeons, should be clearly ascertained, not one suspicion seemed likely to fall upon the ministrant of death. The medicines were never brought to Madame Dalibard, were never given by her hand; nothing ever tasted by the victim could be tracked to her aunt. The helpless condition of the cripple, which Lucretia had assumed, forbade all notion even of her power of movement.

Only in the dead of night when, as she believed, every human eye that could watch her was sealed in sleep, and then in those dark habiliments which (even as might sometimes happen, if the victim herself were awake) a chance ray of light struggling through chink or shutter could scarcely distinguish from the general gloom, did she steal to the chamber and infuse the colourless and tasteless liquid [The celebrated acqua di Tufania (Tufania water) was wholly without taste or colour] in the morning draught, meant to bring strength and healing. Grant that the draught was untouched, that it was examined by the surgeon, that the fell admixture could be detected, suspicion would wander anywhere rather than to that crippled and helpless kinswoman who could not rise from her bed without aid.