The explanation of the mystery about lime-juice (which a hundred years ago was used with absolute success to prevent scurvy, and in 1875 was a dead failure) is shown by the workers at the Lister Institute to be this–namely, "lime" and "lemon" are in origin the same word, and have become applied in ways unrecognized by the Admiralty and their medical advisers in various parts of the world to which the citron, the lemon, the sweet-lime and the sour-lime–all varieties of one species, _Citrus medica_ of Linnæus–have been carried from their original home of origin, the south-east of Asia. The original effective and valuable "_lime_-juice" of the eighteenth century was _lemon_-juice, carefully prepared from lemons in Sicily and Italy, and from 1804 to 1860 in Malta. When the demand for it increased in the nineteenth century, it was adulterated and made up from poor fruit, as the commercial enterprise of contractors and the fatuous incapacity of the naval authorities progressed hand in hand. And then, in the early fifties, the West Indian growers of the small sour-lime (_Citrus medica var. acida_) in Montserrat got the naval contracts, the honest intention of Sir William Burnett, the chief medical officer of the Navy, being to establish a permanent and first-rate supply. Strangely enough, the naval "lime-juice" now really was _lime_-juice and no longer _lemon_-juice. By a natural but fatal misconception, the medical value of the juice, whether of lemon or of lime, was by all authorities attributed to the citric acid present; and the only tests applied to it were chemical ones, and not therapeutic. The Lister Institute Committee have shown by therapeutic experiment–the feeding of guinea-pigs, in which scurvy can be produced and cured at will–that _the anti-scorbutic vitamine remains active and unimpaired in lemon-juice from which all the citric acid has been extracted_. And, further, that the juice of the West Indian sour-lime (_Citrus medica acida_), although very rich in citric acid, _contains only one-fourth the anti-scorbutic vitamine_ which the same quantity of the juice of the true lemon (_Citrus medica limonum_) contains. This has been most carefully established by prolonged series of feeding experiments. It explains the failure of the _lime_-juice in Sir George Nares' Polar Expedition, and restores the confidence in _lemon_-juice based on the unanimous testimony of the early records of its use.