VIRUS GENETICS, MULTIPLICATION, AND PHYSICS 193 



object in between its life inside the host bacterium. It carries, in 

 solution, charged groups which can attach and bind ions to them 

 and so present a specific charged grouping all over its surface 

 in some cases, and at definite spots in other cases. When the 

 right number of ions are bound, the virus can be attracted to the 

 oppositely charged (also specifically grouped) bacterium and 

 there be held by electrostatic forces. While in this condition it 

 can be eluted from the bacterium by changing the ionic strength 

 to one which is not suitable, and agitating strongly. If the tem- 

 perature is right, this kind of attachment is superseded by an 

 enzymatic action which makes a sufficiently large opening for the 

 long and thin nucleoprotein of a virus to enter, while leaving 

 outside a purely protein part which is not concerned with 

 reproduction. 



The organization of the nucleoprotein which has entered is 

 now reduced to a lesser degree, and the process of active multi- 

 plication begins. Because the latent period can be lengthened by 

 damage which does not prevent multiplication, there are pre- 

 sumably nongenetic units present on the entering nucleoprotein. 

 These are quite possibly a group of similar enzyme molecules 

 or enzyme precursors which disperse through the bacterium and 

 start the almost instantaneous change in its metabolic process. 



The genetic part of the virus consists of several units of nu- 

 cleic acid, or nucleoprotein. It is multiple, and some genetic fac- 

 tors are relatively tightly bound together whereas others are 

 readily separable. Before ultimate virus assembly, these units 

 are capable of exchange between individuals. The exchange takes 

 place rapidly and very thoroughly, as four rounds of "mating" 

 can take place in a few minutes. 



Virus construction is concerned with near neighbors, for the 

 exponential growth process requires something like the construc- 

 tion of a new virus, either by growth and division of the old virus, 

 or by the growth of a new one very close indeed to it, certainly 

 close enough to be within the range of some type of molecular 

 forces. 



While this takes place, a steady change of the protein charac- 

 ter in the bacterium goes on and some 300,000 specific molecular 

 protein units are produced, ready to form the outer protein coat- 



