1923] 



DUGGAR & KARRER NATURE OF MOSAIC DISEASE PARTICLES 209 



we have here a group of viruses which, apart from the cell, are as 

 inactive as any colloidal particle lacking that correlated organi- 

 zation which is characteristic of cell life. Within the cell such a 

 virus possesses unusual activity, obviously. So far as resistance 

 to environmental conditions is concerned, we have to admit 

 frankly that there may be no great difference between a living 

 cell, and enzyme, and many types of biocolloids, but, on the 

 whole, the mosaic virus behaves as if it were a biocolloid, yet one 

 endowed with the power of reproduction. Now it has been 

 frequently suggested in the literature that all these discussions 

 as to the nature of a virus are unnecessary, since we may just as 

 well take the easier, simpler view, and call a virus an ultra- 

 microscopic organism. The facts are just a little out of line, if 

 viewed in their broadest aspects; and the fascination is to go on 

 and perhaps ultimately get a satisfactory explanation, or arrive 

 at what may be an acceptable theory. 



We cannot forget that important contributions have been made 

 almost within the year. The d'Herelle phenomenon is itself a 



remarkable discovery. Here is a filterable body — call it what 



you like — appearing in the excretions of dysentery, which, placed 

 in contact with the bacterial culture, is lethal to the culture; and 

 at the same time the body propagates itself. 



Again, if all viruses are minute bacteria, why are there no 

 analogues of such microorganisms as saprophytes? Why are 

 there none in butter, in milk, in soil, in fermentation phenomena 

 of one type or another? While some "indications" of the exist- 

 ence of filterable organisms in such environments have been re- 

 ported, it must be admitted that all changes in such substrates 

 have been related to organisms that are not ultramicroscopic, 

 and no such parallel in nature has been clearly demonstrated so far 

 as I am aware. There are, of course, many diseases induced by 

 extremely small microorganisms but the question is: Have we 

 not already reached the point where our technique may always 

 make evident some stage of such organisms? Are any truly 

 ultramicroscopic organisms culturable? With agencies of the 

 mosaic virus type we have made no progress, possibly because 

 progress is not attainable by culture methods and by micro- 

 scopic vision. 



