You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Key Articles and Guidelines in the Primary Prevention of Ischemic Stroke. Ischemic stroke is a prevalent disease with a large burden on the health system. Preventive strategies, therefore, are paramount. Primary prevention is aimed at reducing the risk of stroke in asymptomatic people. The most effective prevention is through control of modifiable risk factors. Due to the large amount of literature available on this topic, this bibliography (the first of a 2-part series) aims to provide a comprehensive resource for medical practitioners charged with caring for this population.
{"Chemical": []}