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:

A simple, sensitive and accurate method for rat paw volume measurement and its expediency in preclinical animal studies. Several methods are used to evaluate the inflammatory changes. Measurement of edema is the most commonly used method for evaluating artificially induced inflammation in rat model. In this context, we present a method for the measurement of volume of rat paw, in which two glass columns containing fluid are connected by a glass tube. Paw is immersed in one column and the other column is placed on weighing balance. Upon immersion of paw, equal volume of fluid displaced applies a force F, which shows specific and proportional increment in the level of fluid in both the columns, which could then be detected by weighing balance, as 'Force = Weight' of displaced fluid, using the specific gravity of the fluid and the volume of paw, and thus the change in the volume of paw can be calculated. The rat paw immersed in column without touching the wall of the column facilitates the accurate measurement of volume of paw when measured several times. Present method is validated for its accuracy and reproducibility when internal radii of both the columns were same or different. Presented method is also cost-effective and hence can be used for the academic and the commercial animal research purpose, without compromising the precision of the evaluation.
{"Chemical": []}