Functionally regarded, the _nucleus_ is the essential element of the cell. Embedded within the cytoplasm, its isolation therefrom, and this in quantities sufficient for analysis, may well have dismayed the earlier workers. But the resources of Friedrich Miescher were equal thereto. Treating surgical bandages soaked with pus with a dilute solution of sodium sulphate, he extracted the heavy pus cells. These, then, by careful decantation, were easily disengaged. The pus cells, still intact, were then subjected to the digestive action of artificial gastric juice. The protoplasm was thus dissolved, but not the more resistant _nuclei_, which remained as an insoluble grey powder. In this manner cell nuclei, _free from protoplasm_, became available for chemical analysis. Treating the insoluble nuclei thus obtained with dilute sodium carbonate, a solution was formed. Acetic acid added thereto produced a flocculent precipitate which was found to contain phosphorus, and responded to protein colour tests. This substance Miescher christened by the name of _nuclein_. Subsequent observers prepared nuclein from the nuclei of _yeast_ cells and the _red blood corpuscles_ of birds. All nucleins are insoluble acids which form soluble salts with sodium. But while they respond to protein colour reactions they differ from _protein_ in that they contain _phosphorus_ and _resist the solvent action of artificial gastric juice_. Migrating some ten years afterwards (1897) from Tubingen to Basle, Miescher entered upon his celebrated researches into the habits of the Rhine salmon. He found the belief had long been current that the fish, during their passage from the sea up the Rhine to their spawning haunts, never partook of food. That this belief was well founded he was able to prove; for, saving isolated and easily explicable exceptions, he noted that their alimentary canal was devoid of food _débris_, while their digestive juices were as a rule inert. One startling change he noted, that while, on the one hand, their _muscular_ tissue profoundly wasted during their migration, their _organs of reproduction_ enlarged enormously, the inevitable conclusion being that eggs and spermatozoa had been created from muscle protein. RESEARCHES ON SPERMATOZOA Struck by the opportunities for scientific investigation during the spawning season, Miescher determined to resume his work upon _nuclein_. Spermatic fluid or _lachsmilch_, being readily obtainable in great quantities, he had to hand a mass of material admirably adapted for chemical examination of the cell _nucleus_. The conclusion that the _heads_ of the spermatozoa might be regarded as a _metamorphosed nucleus_ seemed obvious, and the opportunity too good to be lost. On examination he found the “sperm heads” protein-free, made up almost entirely of a single chemical entity, a salt of an organic base rich in nitrogen and an organic acid containing phosphorus. The former was _protamine_, the latter _nucleic acid_.