506 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



the collective picture strongly indicates that there is a difference be- 

 tween viruses and ordinary organisms as we know them. 



It is interesting to speculate as to whether or not the fundamental 

 difference is that in the virus proteins we have an example of the 

 vital substance of protoplasm. The virus proteins isolated so far 

 have been found to be nucleo-proteins having unusually high molecular 

 weights. It may be possible that in this chemical combination of 

 nucleic acid and high molecular weight protein we have sufficient 

 organization within a single molecule to endow it with the lifelike 

 properties that characterize it. Such an entity might be regarded 

 as the simplest type of organism, an organism from which all extrane- 

 ous material has been removed and which has become so highly 

 parasitic that it can reproduce only under very special conditions. 

 Green has already pointed out that an intracellular microbe might 

 be expected to undergo a loss of function due to the assumption of 

 such function by the surrounding protoplasm. Such retrograde 

 evolution he states might progress to the point where only a single 

 molecule remains, and this molecule would be expected to possess 

 unusual properties but would be functionally complete only when 

 immersed in protoplasm. We would, therefore, have an entity pos- 

 sessing all the physical and chemical properties of a molecule and at 

 the same time the potential properties of an organism, without it 

 itself being a functionally complete organism. It is obvious that this 

 description fits the virus proteins. It may be that there is something 

 intermediate between such an entity and ordinary living organisms. 

 Studies on some of the larger viruses such as vaccinia should settle 

 this point. Whatever the outcome of these studies, it seems unlikely 

 that they will alter our conception of the smaller viruses; henee we 

 may proceed with our discussion of the virus proteins. 



It is interesting to speculate on the manner in which tobacco mosaic 

 virus protein brings about the production of more of the same kind 

 of molecules when placed in contact with the protoplasm of certain 

 cells. This mechanism is of tremendous importance because it is 

 possible that it or a similar one may be responsible for the production 

 of all the specific protein molecules as well as other molecules within 

 living cells. It may be considered to be the very basis of life. I 

 think we may dismiss at once the mechanism by means of which cells 

 divide and thus reproduce, for we are interested in a more fundamental 

 mechanism, the one by means of which the cell grows until it is in a 

 position for the second mechanism to operate. It seems unlikely to 

 me that the basic mechanism is one in which the virus protein absorbs 

 food, discards waste, grows and at some proper moment divides into 

 two molecules after the manner of cells. A mechanism that I like to 

 consider is one based on the surface forces which Dr. Langmuir has 

 demonstrated so vividly in recent years and some of which he described 



