176 



THE PHYSICS or VIRUSES 



tion are different in the two cases and may account for the differ- 

 ent results. 



The third investigation, that of Malkiel, concerns serological 

 affinity after sonic action. Malkiel studied the precipitin reaction 

 between virus and antisera. The antisera were of two kinds — 

 antinormal TMV and antisonically inactivated TMV. The 

 amount of antibody nitrogen precipitated was plotted as a func- 



0.5 



Sonic treated 

 TMV 



. Control 

 "■^^ TMV 



Aggregated 

 ^ Sonic treated 

 ■\^ TMV 



■^: 



\ 



0.40 

 Mg Nitrogen added per 



0.80 

 ml. antiserum 



1.20 



Fig. 7.3. Affinity between antiserum and TMV, as measured by Malkiel. 

 The sonic treated TMV gives 30% more precipitate than does untreated, 

 and much more than does reaggregated TMV. 



tion of the amount of virus nitrogen added per milliliter anti- 

 serum with the results shown in Fig. 7.3. It can be seen that, for 

 normal virus added to normal antiserum, the amount of precipi- 

 tate increases, flattens, and falls in the usual way as the amount 

 of virus is increased. When the sonic treated virus is used, the 

 amount of precipitate reaches a high value, corresponding to a 

 30% increase over the normal virus. The average virus particle 

 size was measured and was about half the predominant rod 

 length in normal virus. The expected increase in surface area is 

 about 7% for one-quarter-length rods. Thus the increase in area 



