1921] 
DUGGAR & KARRER—SIZES OF MOSAIC DISEASE PARTICLES 355 
minute organisms or propagative parts of organisms in the soil 
or in other products which are commonly the seat of varied 
bacterial activities. While this has been previously pursued in 
certain directions an investigation of one important aspect of 
the problem has been undertaken. This work will be reported 
upon in a subsequent paper. 
No reference has thus far been made to two recent reports by 
Kunkel which are of particular interest in this connection. In 
the earlier paper Kunkel (’21) has studied cytologically the 
tissues of corn affected with a mosaic disease and he reports, 
describes, and figures a foreign body believed to be a living 
organism invariably present in the diseased cells. ‘The distribu- 
tion of this body is found to correspond with the distribution of 
the light green color areas in the diseased leaves. While no 
proof has been afforded that these bodies are etiologically related 
to the corn mosaic, or even that they are living structures, it 
is suggested that they may be more or less analogous to the 
Negri bodies in the brain cells of animals suffering from rabies. 
In a more recent note Kunkel (’22) has associated ameboid 
bodies with the Hippeastrum mosaic, this host plant being a 
member of the Amaryllidaceae. Analogous bodies have not 
thus far been mentioned by those who have studied the mosaic 
disease of tobacco histologically or cytologically. 
It is of course not certain that the mosaic diseases of these 
monocotyledonous plants are caused by organisms or agencies 
similar to those inducing the mosaic of tobacco. At the present 
time either possibility may be entertained. Even should an 
ameboidal structure be found in the cells affected with mosaic 
disease of tobacco and etiologically associated therewith, interest 
in the filtration experiments would remain. Whatever might be 
the size relations of such an organism in the uninjured cell, its 
behavior under filtration would indicate that relatively minute 
colloidal particles of the body are capable of reproducing it. 
A discussion of theoretical aspects is reserved until further 
experimental work has been done.! 
1 Since the above was written the attention of the writers has been drawn to an 
article previously overlooked on a filterable virus, as follows: Andriewski, P. L'ultra- 
filtration et les microbes invisibles. Centralbl. f. Bakt. I. 75: 90-93. 1914. Using 
