THE ORIGIN OF LIVING MATTER 531 



mixture of nonliving matter, then it would be interesting to know 

 if there is a gradual gradation in complexity from the living to 

 the nonliving, that is to say, if it is true that degree of complexity 

 is the only distinction between the living and the nonliving, just 

 when is this degree reached, and are there existent bodies 

 which are intermediate in complexity and therefore belong to 

 neither the one nor the other state? Findlay expressed himself 

 in opposition to this viewpoint when he said that there is no con- 

 tinuity between inanimate and living matter — rather is there 

 a distinct and sharp break in the curve of relations. Life is a 

 new factor — a new set of potentialities— introduced into inani- 

 mate matter. But there is another possibility. Recent work 

 on those remarkable substances known as filterable viruses 

 suggests that they perhaps constitute a link between the living 

 and the nonliving. Bacteriophage is a substance rather like 

 the viruses! Some have said that it is "probably an organism," 

 "self-perpetuating," arising independently in bacterial cultures 

 which it then destroys; others view bacteriophage as a product 

 of the bacterial culture. Then there are the filterable forms 

 of bacteria, which, though filterable, are to be clearly dis- 

 tinguished from the viruses, for the viruses will not grow or 

 multiply on a lifeless medium. The filterable viruses are also 

 intermediate in size between living bacteria and nonliving matter; 

 they come between the largest protein molecules and the smallest 

 living bodies (coccus bacilli). 



Filterable viruses are colloidal, for their aqueous suspensions 

 are turbid (show the Tyndall cone), but their particles are below 

 the limit of ultramicroscopic (dark-field) observation, and they 

 pass through very fine filters. The size of the particle has been 

 estimated to be 25 VQ.^JL, which is about one-tenth the size of the 

 smallest bacillus. Such a particle would consist of 200 to 400 

 protein molecules of average size, which is but five to ten times 

 the diameter of a maximum-sized molecule. The hemoglobin 

 molecule is now estimated to be about 5.5 m^u in diameter. 

 Whether or not viruses are alive is still a debated question, 

 usually answered in the affirmative. A diameter of 25 m/x or a 

 content of some 200 molecules does not leave space or molecules 

 enough for any but relatively simple chemical reactions. But the 

 chemical reactions in the smallest bacterium are probably also 

 less great than in a single tissue cell. 



