Unpublished letter, 'On the structure of the ultimate fibril of the muscle of animal life' from Erasmus Wilson to Peter Mark Roget Using a powerful microscope, Wilson is able to make discoveries on the structure of the ultimate muscular fibril. He records his observations upon a specimen taken from the arm of a strong, healthy man immediately after its amputation. He finds each fibril to be composed of minute cells with flattened surfaces, arranged in a linear series, creating a uniform cylindrical shape. Followed by one page of diagrams regarding the structure of the ultimate fibril of the muscle of animal life. Subject: Biology / Physiology Received 13 June 1844. Communicated by Roget. Whilst the Royal Society declined to publish this paper in full, an abstract of the paper was published in volume 5 of Abstracts of the Papers Printed in the Philosophical Transactions of the Royal Society of London [later Proceedings of the Royal Society] as 'On the Structure of the Ultimate Fibril of the Muscle of Animal Life'. 5 June 1844