384 
that tlie disease could be induced in healthy plants by inoculating them 
with the expressed juice of diseased plants. By rubbing up a plainly 
diseased leaf in a few drops of water, taking up a little of this thick, 
green emulsion in a glass tube drawn out to capillary size, and sticking 
it into the thick midrib of an old leaf so that it remained without 
reaching through to the back side, sound plants became badly diseased 
in nine cases out of ten. The period between the inoculation and the 
first doubtful symptoms was quite regularly ten to eleven days. After 
this period the disease appeared without failure in all the younger 
leaves, i. e., those undeveloped at time of inoculation, and on the small 
shoots which developed in the axils of the diseased leaves. All the 
younger parts of the plants were diseased, exclusive possibly of the 
flowers, and all the older parts healthy. 
It is self-evident that the disease is more severe in proportion to the 
youngness of the plant at the time of inoculation. It is much less 
dependent apx^arently on the quantity of inoculated substance (Impf- 
stoffs ). It is only necessary to be careful that the substance is really 
taken up by the plant, and this is best brought about by using a thin 
fluid and infecting slightly wilted plants. 
After this discovery organized bodies were sought in the sap of the 
diseased plants with new zeal, but owing to the numerous almost color¬ 
less granules normally present in the juice no definite results Avere 
obtained. Some of these granules were not unlike red blood corpuscles, 
but more half-moon shape, Avhile others were smaller. The sap Avas also 
rich in small tetrahedral bodies, which slowly disappeared in HC1, 
and which A\ r ere probably calcium oxalate. The bodies in the sap 
appeared, even AA 7 itli the highest powers, of such indefinite form that 
they could not be identified with any certainty as organized bodies. 
Later Dr. Mayer endeavored to isolate the supposed organisms by 
Koch’s and other methods, and demonstrated bacteria in many cases. 
But none of these, Avhen used for inoculation, caused the disease. He 
also inoculated sound tobacco with various bacteria, dung solutions, 
extract from tobacco, sick earth, etc., but Avithout result. 
The question now arose whether the disease Avas due to an organ¬ 
ized or a chemical ferment. A chemical ferment seemed improbable. 
This sort rarely causes a disease, and it is unheard of that an enzyme 
multiplies from itself. An organized ferment might be a fungus or a 
bacterium. To determine these points the following experiments AA 7 ere 
undertaken: 
The infectious fluids Avere passed through ordinary filter paper 
and the filtrate used for a large number of additional inoculations. 
Itesult: The filtered sap worked almost as well as the unfiltered. The 
per cent of diseased plants Avas only a little less. Either the disease 
was due to chemical substances or else to organized bodies small 
enough to pass through the pores of the paper. A clear filtrate was 
finally obtained by using a double filter, and fluid passed through this 
possessed no infective power. Evidently the cause of the disease Avas 
