May x6,1921 
Bacterial Wilt of Castor Bean 
259 
ISOLATION OF THE CAUSAL ORGANISM 
Such materials as have just been described will almost invariably 
produce pure cultures of the causal organism when proper precaution¬ 
ary measures against external contamination are taken. Repeated 
cultures were made by flaming momentarily the green stalk from a 
wilted plant, then cutting it off with a sterile scalpel and squeezing out 
by means of strong forceps a drop of the plant juice together with the 
bacteria into the tube of beef agar. From this, dilutions were made and 
then plates were poured. This was varied by sterilizing the surface of 
a stalk with mercuric chlorid i to 1,000, girdling it with a circular cut 
and breaking it off, after which sterile conditions were still further in¬ 
sured by searing the edge of the freshly made cut with a red-hot scalpel. 
A hollow could now be made safely in the end of the stalk and a few 
loops of beef broth inserted and mixed with the plant juices. From 
this very thick suspension of bacteria, dilutions were then made for the 
poured plates. 
RESULT OF INOCULATIONS 
As soon as results from the poured plates gave indications that the 
organism in the diseased Ricinus plants was Bacterium solanacearum , 
inoculations were made into tomato plants, which wilted promptly. 
Cultures in other media such as nitrate bouillon (where reduction took 
place) and pink litmus milk (which became and remained blue) also 
served to confirm the diagnosis. From the interior of one of the wilt¬ 
ing tomato plants Petri dish agar poured plates were made and sub¬ 
cultures from some of the colonies were tested out on other tomatoes 
which also wilted (PI. 57). 
By this time Ricinus plants large enough to inoculate were available, 
and a series of inoculations were made by needle on the hypocotyls. 
On these plants the progress of the disease was slower than on the tomato, 
but there was profound dwarfing as a result of the inoculations, and sub¬ 
sequently the plants wilted with bacterial occupation and browning of 
parts of the vascular system (PI. 58-60). From such plants also the 
organism was plated out in practically pure culture. Large Ricinus 
plants also were successfully inoculated by needle pricks (PI. 61). Sub¬ 
sequently the disease was produced on Ricinus by breaking some of the 
roots in soil infected by burying in it Ricinus plants already inoculated 
and swarming with the bacteria (PI. 62). 
We also obtained successful inoculations on a series of jimson weeds 
{Datura stramonium L.), the phenomena in which corresponded exactly 
to results formerly obtained by the senior writer with Bacterium solana¬ 
cearum plated from other plants—that is, wilting, vascular infection, 
brown stain, etc. 
