Much of the difficulty encountered in the chromatographic separation of members of polymeric series is due to the inability of the larger molecules to enter the porous materials used for chromatography. Electrokinetic ultrafiltration was proposed to circumvent this.A preliminary account is now given of experiments with collodion ultrafiltration membranes, where this principle gave useful separations of a series of enzyme-synthesized straight-chain polysaccharides. The data suggest that each membrane excludes molecules exceeding a certain length and that molecules penetrating a membrane undergo simple adsorption on its internal surfaces.
=SUM&Parmi les difficult& dans la separation chromatographique de membres de dries polymhres l'impuissance de grandes mol6cules d'entrer dans les matihres poreuses, employbes en chromatographie, joue un rdle important. L'ultrafiltration blectrocin6tique a 6t6 proposke pour surmonter cette difficult& Nous prdsentons ici un rapport preliminaire d 'exp6riences avec des membranes de collodion pour ultrafiltration, ou ce principe donnait des ¶tions avantageuses d'une s6rie de polysaccharides de chaine linbaire, synth6tisbs par des enzymes. Les rksultats font supposer que chaque membrane exclut les molbcules excedant une certaine longueur et que les mol6cules pknktrant une membrane subissent une adsorption simple sur les surfaces internes de la membrane.
ZUSAMMENFASSUNGEine der Hauptschwierigkeiten bei der chromatographischen Trennung von Gliedern polymerer Reihen liegt in der Unfahigkeit der grosseren Molekule in die porosen Materialien, wie sie fur Chromatographie venvendet werden, einzudringen. Die elektrokinetische Ultrafiltration wurde zu deren Uberwindung vorgeschlagen.Ein vorlaufiger Bericht iiber Untersuchungen mit Kollodium-Ultrafiltrationsmembranen wird hier gegeben, wobei dieses Prinzip brauchbare Trennungen einer Reihe geradkettiger Polysaccharide, die durch enzymatische Synthese erhalten.worden waren, gab. Die Resultate geben zu der Vermutung Anlass, dass j ede Membran Molekiile, die eine gewisse Lange uberschreiten, aufhalt, und dass Molekiile, die eine Membran durchdringen, einfache Adsorption an deren inneren Oberflachen erfahren.
1. Nitrogen-balance experiments showed that casein supplements fed to hill ewes on a low plane of nutrition in the later stages of pregnancy were used very ineffectively, despite the animals' need for protein.2. In confirmation of McDonald (1948a, b, 1952) extensive conversion of casein to ammonia was found to occur in the rumen, with absorption of ammonia into the blood stream.3. Casein administered to sheep by duodenal fistual was better utilized than when administered by ruminal fistula.4. The course of dissolution in the rumen of casein in the form of tough lumps was observed by a staining procedure.5. It was found possible to process casein in a way that led to better utilization as shown by nitrogenbalance experiments. This processed casein gave less ammonia in the rumen.6. It is concluded that the formation in the rumen of ammonia from proteins may be an important factor determining their usefulness to the animal. Processing may have effects on the value of a protein for ruminants quite different from those on the value for non-ruminants. The tendency to value proteins for ruminants solely in terms of their digestibility is criticized, and it is suggested that casein has disadvantages as a ‘standard protein’ in nutrition experiments with ruminants.
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