The author commenced his memoir by observing, that about two years ago, he read to the Society some observations respecting an entozoon, of a very singular nature, occurring amongst the human muscles, a species of minute, and indeed microscopic, vibrio. The merit of the discovery was due to Messrs Hilton and Paget of London. Dr Farre afterwards gave an account of its internal structure. Soon afterwards it was announced, that this peculiar entozoon had occurred in other dissecting rooms—in Bristol, for example, and in Dublin. It was added, that the occurrence was rather frequent, in Dublin particularly, and that its existence amongst the human muscles seemed traceable to previous debility and exhaustion of the person before death had occurred. The author of the present memoir is, however, of opinion, that neither of these points has been made out clearly.