42 BERGOLD 



sibility is very unlikely, although a similar process takes place at the 

 sporulation of Clostridium tetani when the rod-like fusion nucleus 

 changes into a small sphere (Bisset, 1950). The second possibility may 

 be supported by the following argument: 



If only one rod develops from one, no multiplication takes place at 

 all. In the silkworm virus the double rods occur infrequently and the 

 rapid increase of the virus particles can hardly be explained. It is 

 therefore possible that a single rod contains smaller sub-units which can 

 develop into rods. If virus rods are suspended in 0.05 M. HCl small 

 spherical bodies become visible. This is of course no proof, it may be 

 just an artifact due to denaturation. There is good hope of showing 

 sub-units also in untreated rods applying shadow casting. I have ap- 

 plied several methods to divide the rods into sub-units and check their 

 infectivity, but without success. The existence of sub-units has been 

 suggested in other viruses too (Luria, 1947, Putnam and Kozloff, 1950). 



The developing stages of another insect virus, the polyhedral virus 

 of the spruce budworm, are similar to those from the silkworm. Double 

 rods are more frequent here. Bundles or developing stages and mature 

 rods seem to be present at the same time in one polyhedral body. 



The development of the polyhedral virus of the gypsy moth is a 

 little different since usually four rods develop in a bundle arrangement. 

 Again the early spherical stages and the curved "germ" within the 

 membrane which seems to undergo heavy internal structural changes. 

 Lengthwise fission is the rule here, but sometimes narrow forms with 

 probably only one rod can be found. Finally usually four mature rods 

 slip out of the membranes. In partly dissolved polyhedral bodies many 

 empty pockets can easily be seen from which the virus bundles have 

 slipped out. 



The second type of insect viruses we know of is the capsule virus 

 (Bergold, 1948b). In contrast to the polyhedral virus, the inclusion 

 bodies are egg shaped and much smaller, that is only about 360 x 230 

 millimicrons. Each capsule contains only one virus rod or a double rod. 

 The rods slip out when the capsule is dissolved in alkali. In spite of 

 these differences, the development of the rods is similar to the poly- 

 hedral virus. Again the early spherical stages, the straightening out of 

 the "germ" inside the membrane, and the double forms. The mature 

 rods are somewhat different: wider and usually slightly bent. In such 

 capsule virus suspension I have never observed tube shaped membranes. 



The "life cycle" and the complicated nature of development and 

 multiplication indicate that insect viruses are organisms with spherical 



