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:

Letter to the Editor: Prescience of a Surgeon in 1980. A photo copy of a page from an unpublished document written in 1980 by the surgeon Mr. Selwyn Taylor and entitled "The Thyroid and the Thymus", provides remarkable prescience concerning thyroid lymphocytic infiltrates in Graves' disease and the implications for treating or resolving exophthalmos.
{"Chemical": []}