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.
The presence of this salt protamine nucleate led to the conclusion that nuclein was merely a salt of protein and nucleic acid.
The Discovery of Purins
Miescher, who had already isolated nuclein and nucleic acid, came nigh to one other equally important discovery. Heating a specimen of protamine with nitric acid, he noted that a yellow spot formed which turned to bright red when moistened with alkali.
Alive to the import of the reaction, Miescher requested Piccard to examine salmon sperm for purin bases. Extracting the same with hydrochloric acid, Piccard found guanine, and what he thought was hypoxanthine, but which was in truth adenine.
Another distinguished worker in this sphere, Kossel, noted that, subjected to the action of hydrolytic agents, nucleins always yield purin derivatives; also that the same were derived, not from the protein of the nuclein, but from the nucleic acid. Thus it was to Kossel that we are indebted for the discovery of the purin bases, hypoxanthine, xanthine, guanine, and lastly adenine. It was, indeed, through his brilliant achievements that nucleic acid became recognisable as a definite entity, distinguishable from proteins and other body elements, this latter differentiation by token of the purin bases which are contained in nucleic acid.
Moreover, it led to the dissipation of the old belief that uric acid was an intermediate product of protein metabolism, for the revelation of purin bases as decomposition products of nucleic acid carried with it the inference that uric acid also had chemical affinities therewith. The chemical structure of the purin bases and that of uric acid betrayed a common likeness, and, therefore, a presumptive physiological connection; in other words, that a chemical nexus obtained between the cell nucleus or nucleic acid and uric acid.