22 
BULLETIN 879, U. S. DEPARTMENT OF AGRICULTURE. 
of inoculations with diluted juices of mosaic cucumber plants. 
Allard (2) showed that the virus of tobacco mosaic could be diluted 
to 1:1,000 without reducing its virulence. He also made a number 
of successful inoculations with the dilutions of 1:10,000, although 
higher dilutions rarely gave infection. The work of the writer with 
cucumber mosaic has given similar results, as is shown in Table TV. 
The juices of mosaic plants were expressed, filtered through filter 
paper, diluted with sterile distilled water up to 1:100,000, and used 
for inoculating healthy plants. These experiments show that dilu- 
tions of 1:1,000 are as potent as undiluted solutions, but while 
infections may result from those of 1 : 10,000 they have never taken 
place at higher dilutions. In all of this work inoculations were made 
at the base of the stem and in two or three of the younger leaves, 
the latter being inoculated at two or three points by pricking a drop 
of the solution into the leaf. Stems were cut slightly and the cut 
surface was covered with a drop of the diluted virus. 
Table IV. — Effect of dilution with sterile distilled water on the power of infection of the 
expressed juices of mosaic cucumber plants. 
Date inoculated. 
Series I: 
Apr. 8, 1916. 
Do 
Do 
Do 
Do 
Series II: 
Sept. 8, 1916. 
Do 
Do 
Do 
Do 
Series III: 
May 15, 1917 
Do 
Do 
Do 
Do 
Number 
Dilution of expressed juices. ^^ 
lated. 
Undiluted. 
1:100 
1:1,000 
1:10,000.... 
1:100,000... 
Undiluted. 
1:100 
1:1,000 
1:10,000.... 
1:100,000... 
Undiluted. 
1:100 
1:1,000 
1:10,000.... 
1:100,000... 
Results. 
Number 
of mo- 
saic 
plants. 
Disease 
noted 
(date). 
Apr. 20,1916 
Do. 
Do. 
Do. 
Sept. 18,1916 
Do. 
Do. 
May 23,1916. 
Do. 
Do. 
Do. 
The regularity of infection which follows inoculation with dilutions 
of 1:1,000, together with the numerous infections at 1:10,000, shows 
an apparent power of rapid increase in the infectious material present 
in mosaic plants, since in these cases the period of incubation was no 
longer than when the undiluted juices were used. 
EFFECT OF VARIOUS CHEMICALS ON THE VIRUS. 
Experiments with the effect of various chemicals on the virus of 
cucurbit mosaic show that the power of infection is easily destroyed 
by common disinfectants and antiseptics. In this work the juices 
of mosaic cucumber plants were expressed and filtered through filter 
paper. The extract was put into test tubes in 5 c. c. portions and 
