INSECT VIRUSES 4I 



glutamic, serine, glycine, threonine, alanine, methionine, tyrosine 

 (small), valine, leucine + isoleucine + phenylalanine, proline (small), 

 lysine, arginine, histidine. 



The sedimentation curve of virus suspensions, obtained in the ultra- 

 centrifuge, are rather wide or show even different fast sedimenting 

 components. This means that the virus particles are not homogeneous 

 in size (Bergold, 1948a). 



Extensive observations in different electron microscopes of many 

 different preparations of four different viruses confirmed this assump- 

 tion, showing different morphological forms of virus sizes. It led finally 

 to the discovery of a development cycle (Bergold, 1950). Different 

 developing forms have been discussed also in other viruses (Hoyle, 

 1948, Heinmets and Golub, 1948, Bang, 1948, Markham, Matthews and 

 Smith, 1948, Horsfall, 1949). I would like to repeat that the starting 

 material for these insect virus preparations was very well purified 

 crystalline polyhedral bodies, dissolved in weak alkaline. The only 

 possible inclusions must originate in components of nuclear or virus 

 material. Since Trager (1935) has shown in tissue cultures that the 

 polyhedra develop within a few hours, it seems possible that various 

 developing stages of the viruses are occluded and liberated when the 

 polyhedral bodies are dissolved in alkaline. From several hundred pic- 

 tures a sequence has been selected which was probable from the view- 

 point of morphological development. The continuity of morphological 

 characteristics gives strong evidence that we are dealing with the virus. 



The early stages, growing from unknown size, are spherical. The 

 "germ" elongates and curves as it develops within an outer spherical 

 membrane. As it grows it straightens out to a more rod shaped particle. 

 While still in the membrane it shrinks in width and the rod finally 

 leaves the spherical and a tube shaped membrane. It can not be decided 

 yet, whether the rods slip out of the tubular membrane due to the high 

 vacuum in the electron microscope or whether it happens under natural 

 conditions. The characteristic breakage of the empty membranes con- 

 firms their reality. Without any comments I would like to recall to your 

 mind the "ghosts" of some bacteriophages, which proved to be mem- 

 branes (Anderson, 1949). The spherical membrane of the insect virus 

 particles confirms the connection between the spherical developing 

 forms and the mature rods. Sometimes a lengthwise groove in a rod is 

 visible. This leads to the question of multiplication. 



We do not know how the rod shaped particles begin again to mul- 

 tiply. Two possibilities are suggested. Either the rod shaped particle 

 shrinks to a small sphere or it contains several sub-units. The first pos- 



