Although under difficult conditions, the work at the Netherlands Indies Rubber Research Institute at Buitenzorg (Java) was continued during the Japanese occupation. Since it will be a long time before the accumulated results of the years 1942–45 can be published in detail, some points of general interest are reported here. It is common knowledge that, on addition of small amounts of salts of bior polyvalent cations to fresh latex, partial coagulation follows. The yellow colored coagulum generally contains 10–30 per cent of the rubber and after drying gives a yellow rubber, rich in proteins, and having a high acetone extract. The high acetone extract and the color are produced by the yellow particles, first observed by Frey-Wyssling, which, although generally called “resin particles”, contain mainly lipoids. What, however, is the reason for the high protein content? In 1941 it was observed by one of us (L.N.S.H.) that when fresh latex is centrifuged in tubes, a separation occurs into a heavy yellow fraction, taking up a tenth to a third of the total volume, and a lighter white fraction. The yellow fraction is more viscous and often in itself consists of various layers, bright yellow, gray yellow, orange, or even green. Much information was obtained by studying separately the chemical composition, colloid-chemical and enzymological properties of these fractions.

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