1917] 
FREIBERG—MOSAIC DISEASES 215 
was the result of a chemical reaction; and the reason for the 
destruction of the infective principle at a concentration of 
1:800 is that it required this quantity of formaldehyde to 
balance the reaction. Glycerin, in varying concentrations, is 
frequently used as an extractive for enzymes. The solution 
of the enzyme actually takes place in the water, but the use 
of glycerin is advantageous on account of its penetrating 
power and preservative properties. 
The other extractives employed by Allard, when used in 
connection with enzyme work, are used only as preservatives. 
The fact that the infective principle can be extracted only 
with water is in accordance with the common practice of secur- 
ing enzymes by dissolving them in water or obtaining them 
as aqueous extracts. The action of the alcohol on the dried 
material was two-fold. In the first place, it had a tendency 
to precipitate the enzyme in the tissue, thus making subse- 
quent extraction impossible, and in the second place, the 
alcohol exerted a destructive influence upon the enzyme. 
Allard also treated green tissue with extractives. In these 
cases he was able to extract the infective principle at least to 
some degree. However, this should be regarded as a solu- 
tion of the enzyme in the water naturally present in the plant, 
the extractives merely acting as antiseptics. 
It was also found that the ‘‘virus’’ could be thrown out 
of suspension with precipitates of aluminium hydroxide and 
nickel hydroxide. This merely demonstrates the familiar 
process of flocking out colloidal suspensions and is entirely 
applicable to enzyme solutions. 
The effect of heat was tested on both wet and dry material. 
Extracts, according to the results of early workers, lose their 
infectious properties at 65-75° C. Although this is the lethal 
temperature for many organisms, it is also the temperature 
at which most enzymes are deactivated. Allard states that 
“Ше infective principle of the virus is quickly and perma- 
nently destroyed at temperatures near the boiling point. . . ."' 
This is not only applicable to enzymes but also to other com- 
pounds readily undergoing hydrolysis. Dried heat destroyed 
the infective principle of dry material at 130° C., but Allard's 
