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Abstract
Summary: The ciliate Paramecium caudatum was cultivated in a medium consisting principally of known chemical compounds, including 17 amino acids, guanylic, adenylic, cytidylic and uridylic acids, sodium acetate and sodium pyruvate, linoleic and oleic acids, a mixture of B vitamins and several inorganic salts. In addition it was necessary to add microgram quantities of a protein concentrate, first obtained from autolysed yeast, but recently by an improved method from dried green peas. Lipids were first extracted from the crude material and the protein was then dissolved and precipitated with 10% trichloroacetic acid. This protein was further purified by paper chromatography to yield a concentrate active in dilutions as low as 10 μg./ml. When the protein was hydrolysed enzymically or by acid or alkali, the hydrolysates were inactive. Sixteen amino acids were qualitatively identified in the hydrolysate. The nutritional role of a protein effective in such small concentrations has not yet been satisfactorily explained.
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