Read carefully a brief summary of one of the investigations of Sherlock Holmes: While investigating the murders of Stangerson and Enoch Drebber he got into conversation with fellow detectives which runs as follows: 'The last link _______ My case is complete _______ could you lay your hands upon those pills'. After he got those pills - Holmes cut none of them - dissolved it in water and placed it in front of the terrier. Contrary to his expectations - the animal survived - though disappointed a bit - he thought for a while and then cut the other pill - dissolved it - added milk and placed before the animal. The moment it licked - the animal died. Those were the pills present at the scenes of crime. Which one of the following aptly describes the methods which this passage indicates?