666 



Journal of Agricultural Research 



Vol. VI, No. 17 



Table XIII. — Effect of heat upon the infectivity of mosaic virus which has been evapo- 

 rated to dryness at room temperatures in IQ15, 10 plants having been used in each test 



From the data in Table XIII it is evident that the evaporated virus 

 solution lost its infectious properties much more quickly than the dried 

 and ground mosaic leaf material. Likewise, the peroxidase was some- 

 what more quickly destroyed in the evaporated material. Although the 

 presence of small amounts of moisture in the air-dried residue of the 

 evaporated virus may have hastened the destruction of the infective 

 principle in this material, it is also possible that the infective principle is 

 better able to withstand high temperatures when allowed to remain 

 within the tissues of the leaf. 



Although the virus with which Koning (14, p. 71-86) worked appears 

 to have withstood temperatures as high as ioo° C, the virus with which 

 the writer worked is very quickly destroyed at temperatures above 90 . 

 In some instances, however, the virus has been rendered noninfec- 

 tious at a temperature 10 degrees lower than this. These results were 

 obtained with the virus designated as X 16 . This virus was extracted 

 from tobacco plants on September 20, 191 5, and bottled until used on 

 October 18, 191 5. Although the unheated virus was highly infectious, 

 the. infective principle was destroyed after heating for 5 minutes at 8o°. 

 It was also destroyed when heated for 2 minutes at 8i°. Although the 

 original, unheated virus gave intense reactions for catalase and peroxi- 

 dase, the catalase was completely destroyed in these tests. Weak peroxi- 

 dase reactions, however, were again shown the next day. 



As Woods (20) has shown, there is frequently a return of peroxidase 

 activity in solutions of virus that have been once heated. This activity 

 does not appear to return immediately after cooling, but usually requires 

 some hours for its return. Woods considered that the enzyn was de- 

 stroyed in such solutions but a resistant zymogen again generated more 

 of the peroxidase after cooling. On the other hand, Hasselbring and 

 Alsberg (9) were led to believe from their experiments that a zymogen 

 might not be present, but that the enzym was included and protected in 

 the coagulum and subsequently leached out on standing. 



By heating the virus several times at 85 ° C, the writer has been able 

 in some instances to destroy completely the peroxidase present without 

 destroying the infective principle. The highly infectious virus desig- 

 nated as X° and showing intense peroxidase reactions was treated as 



