100 YEARS AGO

When the pseudopodium of an Amoeba has reached a certain development it suddenly retracts, or rather collapses, for [in this book] Kassowitz regards the phenomenon as a rapid tumbling to pieces of the molecular structure owing to stimulation: certain protoplasm-molecules are shattered, atom-groupings of carbon and hydrogen split the molecular oxygen and are at once burnt to CO2 and OH2, the heat-vibrations evolved during the combustion shattering more molecules, and so on, throughout that part of the mass. This process exhausted, a period of restitution sets in, and new molecules are built up from the fragments of proteids, carbohydrates, fats and mineral substances at disposal, and become interpolated between those which had escaped destruction, and a new pseudopodium is put out by assimilative growth. Among other arguments for the view that this is really a process of growth, Kassowitz points out that the rate of protrusion of such a pseudopodium, rapid as it appears under a high power, is really not much more rapid than the growth of a stem of asparagus, a mushroom or a bamboo.

From Nature 5 July 1900.

50 YEARS AGO

It is the purpose of this communication to describe a novel chromatographic method of using ion-exchange resins so that only one of two possible adsorption mechanisms associated with their use can function. Weak organic electrolytes and, in particular, aromatic organic ions can be adsorbed on an ion-exchange resin by a combination of salt linkages and Van der Waals' adsorption forces, if the electrical charge of the resin has the opposite sign to that of the organic ions. Partridge and Davies have recently… shown that a major limitation of ion-exchange resins to-day is their inability to fractionate mixtures containing aromatic molecules. It is suggested that these difficulties can be resolved if aromatic molecules are adsorbed on a dissociated ion-exchange resin the electrical charge of which has the same sign as the aromatic ions. Under these conditions only the undissociated aromatic molecules can be adsorbed, since the corresponding ions cannot approach the surface against its repulsive electrostatic forces. Any change in the pH which dissociates the adsorbed aromatic molecules will result in their desorption. D. E. Weiss

From Nature 8 July 1950.