162 
The Ohio Naturalist. 
[Vol. XIII, No. 8, 
He describes the bacterium which he used successfully for 
inoculation purposes, but did not make thorough studies of its 
habits. It is 0.3 mic. long; in fresh cultures it forms quite long- 
threads or chains. It may liquify gelatin under certain conditions, 
staining it black. He concludes by saying, that the question of 
the artificial culture of this microbe of mosaic disease needs further 
study. Hunger (1905), however, reports that he succeeded at 
times in obtaining minute bodies which he says might be taken 
for bacteria. But he says (p. 264), “In fact, I was able to obtain 
minute bodies at times following out the technique in a few cases 
even the plasmodium-like bodies. Unfortunately, however, I 
cannot regard these as bacteria or zoogloa, since it is shown that 
both of these bodies disappear when phenolchloralhydrate is 
used in connection with heat, all remaining cell structures remain 
undisturbed.” In a recent article, Allard (1912), believes that 
Aphids are carriers of mosaic disease in case of tobacco. Accord¬ 
ing to his experiments, he would not place this malady in the 
category of purely physiological diseases. He says, that facts at 
hand strongly suggest the presence of a living, active micro¬ 
organism. 
In order to reach definite conclusions in a pathological problem 
of this nature, experiments must be conducted on an extensive 
scale. The organism should be isolated, grown on various media 
and its cultural characteristics properly recorded. Proper checks 
with inoculation experiments are absolutely necessary. An ex¬ 
periment without accompanying controls is of little value. The 
original organism must be reisolated after inoculation and its 
presence conclusively demonstrated in the host, before its con¬ 
nection with the disease can be considered established. Inasmuch 
as this has by no means been accomplished, the bacterial theory 
cannot be considered as more than a working hypothesis. 
2. The Virus Theory .—The “contagium vivium fluidum” 
or virus theory seems to be a kind of variation of the bacterial 
theory. Beyerinek (1898) abandoned the bacterial theory and 
proposed this in its place. He says (p. 5), “this is not brought 
about by a microbe, but through a “contagium vivium fluidum.” 
He regards the virus as a soluble substance and not a corpuscular 
body. It remains inert in dead organic material, but when mixed 
with the cell plasma, it increases in quantity, but docs not lose 
its individuality, hence the name. He regards the Flecken- 
krankheit of tobacco as a mild form of the disease, largely con¬ 
fined to the chloroplasts, while in the more intensive forms the 
protoplast as a whole is involved. His theory is based upon two 
considerations. (1). The virus must be a liquid and not a 
corpuscular body, because it diffuses through agar, which is im¬ 
possible for a corpuscular body. (2). He believes that it must 
increase in the plant, because a small drop causes numerous 
