[Vor. 4 
212 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
are ‘‘physiological’’ in origin, then any physical condition 
which would accelerate a particular type of chemical reaction 
would tend to make the disease more pronounced. 
It was not until July, 1916, that any experiments were re- 
ported on the properties of the infective principle of mosaic 
diseases. Allard (716%) at this time reported on a set of ex- 
periments which he interpreted as further evidence in favor 
of his view that mosaic diseases are due to a filterable para- 
site or **virus." His results are in brief as follows: 
A number of filtration experiments were carried on, from 
the results of which Allard concluded that the organism was 
filtered out. These results can, however, be explained on an 
entirely different basis. Lacking a Berkefeld filter, he filtered 
the extract through a Livingston atmometer porous cup. It 
was found that the resulting filtrate contained no infectious 
substance. Although one might conclude that if an organism 
had been present, it was filtered off, it nevertheless does not 
preclude the possibility that a colloidal compound or enzyme, 
because of its relatively large particles or partial absorptive 
phenomena, might not also have been arrested by the filter. 
The extract was next filtered through powdered tale. It was 
found that if a certain amount of extract was filtered through 
a certain amount of tale, a stage was reached at which all of 
the infectious properties were filtered off. However, on 
studying the data, we notice that the oxidase activity was 
also destroyed entirely or reduced correspondingly. This 
should therefore not be interpreted as a simple filtration ex- 
periment with an organism, but as an illustration of the high 
absorptive properties possessed by colloids in general and 
therefore by enzymes, such as the oxidases and probably the 
infective principle of mosaic diseases. 
Precipitation experiments with ethyl alcohol were also саг- 
ried out by Allard. For this purpose 45, 50, 75, and 80 per 
cent alcohols were used. In each case a certain amount of ex- 
tract was taken and enough absolute alcohol added to give 
the desired concentration. The mixture was allowed to stand 
from 1 to 2 days, at the end of which time the precipitate was 
filtered off and dried at room temperature. Suspensions of 
