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solutions of the virus protein the large molecules seem to disintegrate 

 with the formation of smaller units that are more resistant to sediment- 

 ation. 



A highly important point is, moreover, that most preparations ev- 

 idently contain small amounts of nucleic acids, although these can be 

 eliminated by dialysis under special conditions without thereby causing 

 any loss in virus activity. 



Apart from the causal agents of the above-mentioned plant virus 

 diseases yet another virus has been obtained in a state of sufficient con- 

 centration and purity to permit some account concerning its comp- 

 osition. This is the coli bacteriophage which Schlesinger isolated in 

 virtually pure, though not crystalline state. Also this preparation ap- 

 peared to be a protein. The most characteristic analytical result was 

 the high phosphorus content (3.7 per cent) ; this, together with the 

 later reported positive outcome of the Feulgen test, leads to the con- 

 clusion that the bacteriophage is, at least predominantly, composed of 

 nucleoprotein. The virus of foot-and-mouth disease, far more difficult 

 to isolate in large amounts, has been shown by Janssen to be a phos- 

 phorus-containing protein as well. Noteworthy is furthermore that 

 Schtiler could ascertain with a very concentrated and active bacterio- 

 phage preparation that this material does not by itself exhibit any 

 metabolic activity; in media with organic substrates but devoid of 

 bacteria it causes neither consumption of oxygen, nor production of 

 carbonic or other acids. 



In summary we may therefore conclude that observations in var- 

 ious directions converge in the concept that at least the smaller viruses 

 are high-molecular proteins, attached more or less firmly to nucle- 

 otides or nucleic acids. 



It is now possible to formulate somewhat more clearly the problem 

 confronting the biochemists in relation to these results in the following 

 manner : what factors determine the synthesis of this group of com- 

 pounds in the host cells? This is a question that at first sight seems so 

 stupendous that one might well despair of ever finding an answer to it. 

 Nevertheless, here, too, one can discern a spot of light; because a more 

 careful consideration makes it clear that the synthesis of a virus protein 

 is not an isolated problem ; ultimately it belongs to the same category 

 as the problem of biochemical synthesis in general. 



Now it is a most remarkable fact that virtually all biologists consider 



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