As soon as we had satisfied ourselves of the susceptibility of the monkey to inoculation with measles1 we turned our attention to the study of the nature of the virus as it exists in the circulating blood. Accordingly we made experiments to determine its filterability, its resistance to drying, heat, freezing and "age," and now desire to present briefly some of our results, reserving greater detail for publication in a bulletin that will cover all of our work.
We have made four separate attempts to determine this point. In each case the blood-serum was obtained by centrifugation of defibrinated blood and was diluted with three volumes of saline solution before filtering through a Berkefeld candle.Our first two experiments appeared to be negative. In our third experiment we inoculated four monkeys with filtered serum which on account of an accident we had been obliged to pass through two Berkefeld