The Isolation of Nucleic Acid
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.