10 F. M. BURNET AND W. M. STANLEY 



For many of the most Immanly important aspects of virology we must be 

 content at present, and perhaps for many years, with providmg concepts 

 that have provisional value in making it easier for students of the phenomena 

 to predict the result of changing circumstances. Some, but by no means all, 

 of these concepts can in principle be expressed quantitatively and the general 

 objective will be to bring more and more phenomena into a quantitative mold. 



Probably all experimental biologists will agree that this is the most desir- 

 able approach and, to a very considerable extent, the topics chosen for study 

 are chosen because it seems likely that they will be amenable to quantitative 

 study. Many biologists will, however, suffer serious doubts about the ade- 

 quacy of such a view and even experience at times a sense of the futility of a 

 vast amount of quantitative biological research. A small amomit of virus is 

 inoculated into a susceptible system — mouse brain, allantoic cavity, or tissue 

 culture. In some hours' time there is present in the system much more virus 

 than was added to it. This phenomenon presents a multitude of aspects, but 

 at the simplest level we can ask what are the factors which determine the 

 yield of virus in relation to time since inoculation. To be more specific, let us 

 take the example of influenza virus inoculated into the allantoic cavity — a 

 minimal infective dose increases to say 10^^ infective doses after 48 hours at 

 35°C. This process has been extensively investigated at a high level of tech- 

 nical skill but the final result may be fairly expressed in the statement that 

 "after a variable lag of a few hours an approximately logarithmic increase of 

 virus proceeds for about 20 hours followed by a slow final rise which is 

 eventually balanced by thermal degradation of virus." 



The best way of exemjilifying our third objective, of expressing the relation 

 of the phenomenon studied to other phenomenon in the simplest acceptable 

 form, is to list some of the more "interesting" aspects of this same process of 

 influenza virus multiplication in the allantoic cavity. An interesting aspect 

 might be defined as one which, in addition to providing an experimental 

 situation for which parameters can be defined with at least some precision, 

 also appears capable of logical relation to other experimentally accessible 

 aspects of the whole process. 



The chief interest of such a list is the opportunity it offers to consider the 

 extremely wide range of concepts in which provisionally valuable scientific 

 generalizations are being made. Under each of the aspects listed a brief 

 comment is given on the type of provisional generalization that has emerged. 



1. Adsorption to the cell surface and entry into the cell, of which the first 

 phase is mediated by adsorption of a virus constituent of enzymatic char- 

 acter, a neuraminidase according to Gottschalk (1957), to its substrate in one 

 of the prosthetic groups of a cell surface mucoprotein molecule with, in 

 addition, a variety of ionic and other adsorptive forces playing a part in the 

 attachment. 



