RT Journal T1 HAndbuch der virusforschung JF Journal of the American Medical Association JO Journal of the American Medical Association YR 1939 FD July 1 VO 113 IS 1 SP 85 OP 86 DO 10.1001/jama.1939.02800260087034 UL http://dx.doi.org/10.1001/jama.1939.02800260087034 AB This is a collective work by a most competent group of specialists in a field of remarkable activity, of astounding results and of greatest scientific significance. The viruses lie at the lowest margin of the living world or beyond it, depending on the concept of the limits of living substance. They appear to be protein substances capable of self propagation within living cells and to be composed of units mostly but not wholly beyond the limits of visibility or photographic detection even with the ultramicroscope. They can be centrifuged, filtered through graded collodion membranes, purified by filtration and high speed centrifugation from organic contaminants, and inactivated and reactivated by various chemical procedures. Their dimensions can be determined within limits and their activity retained between a series of crystallizations. They differ among themselves not only in their pathologic consequences but in dimensions and in physical and chemical properties. They can be