The guiding fact of pisciculture has been more than once accidentally re-discovered—that is, allowing that the ancient Romans knew it exactly as now practised; but nothing came of such discoveries, and till a discovery be turned to some practical use, it is, in a sense, no discovery at all. After being lost for many hundred years, the art of artificially spawning fish was re-discovered in Germany by one Jacobi, and practised on some trout more than a century ago. This gentleman not only practised pisciculture himself, but wrote essays on the subject as well. His elaborate treatise on the art of fish-culture was written in the German language, but also translated into Latin, and inserted by Duhamel du Monceau, in his _General Treatise on Fishes_. Jacobi, who practised the art for thirty years, was not satisfied with a mere discovery, but at once turned what he had discovered to practical account, and, in the time of Jacobi, great attention was devoted to pisciculture by various gentlemen of scientific eminence. Count Goldstein, a savan of the period, likewise wrote on the subject. The Journal of Hanover also had papers on this art, and an account of Jacobi’s proceedings was enrolled in the Memoirs of the Royal Academy of Berlin. This discovery of Jacobi was the simple result of keen observation of the natural action of the breeding salmon. Observing that the process of impregnation was entirely an external act, he saw at once that this could be easily imitated by careful manipulation; so that, by conducting artificial hatching on a large scale, a constant and unfailing supply of fish might readily be obtained. The results arrived at by Jacobi were of vast importance, and obtained not only the recognition of his government, but also the more solid reward of a pension. I need not detail the experiments of Jacobi, as they are very similar to those of others that I intend to describe at full length in this portion of my narrative.