178 
Journal oj Agricultural Research 
Vol. XXX, No. 2 
Table I .—Comparative germination and growth rate of spores of Colletotrichum 
circinans and Botrytis allii of different ages in relation to the volatile substances 
from onion juice ° 
Age of 
Number of drops of onion juice in chamber— 
culture 
Organism 
from 
which 
f 
1 
1 
Con¬ 
trol 
spores 
were 
secured 
5 
4 
3 
2 
1 
0.5 
0.1 
0.01 
0.001 
Days 
[Germination (per cent)__ 
93 
88 
93 
93 
91 
94 
95 
91 
93 
95 
3 
Length of germ tubes 
49 
73 
106 
108 
144 
132 
167 
165 
164 
170 
(microns). 
Colletotrichum 
Germination (per cent)„ 
0 
0 
2 
7 
98 
98 
96 
99 
100 
99 
circinans. 
29 
■{Length of germ tubes 
0 
0 
41 
36 
53 
66 
79 
70 
74 
(microns). 
Germination (per cent) _. 
0 
0 
2 
0 
46 
44 
39 
32 
60 
44 
77 
■{Length of germ tubes 
0 
0 
31 
0 
50 
63 
50 
53 
45 
52 
(microns). 
Germination (per cent) __ 
78 
71 
98 
96 
86 
92 
91 
86 
84 
97 
4 
Length of germ tubes 
39 
39 
69 
74 
115 
149 
180 
171 
191 
180 
Botrytis allii . 
(microns). 
Germination (per cent) 
49 
67 
63 
78 
85 
88 
92 
85 
79 
85 
28 
Length of germ tubes 
18 
18 
25 
26 
37 
42 
53 
50 
57 
60 
(microns). 
•Duration of experiment, 13 hours at room temperature. 
EFFECT OF HEATING THE EXTRACT 
The effect of heat upon the toxicity 
of onion juice was studied. It was 
reported earlier by the senior author ( 1) 
that in onion juice which had been 
heated in live steam for 20 minutes the 
spores of Colletotrichum circinans germ¬ 
inated and the mycelium grew rapidly. 
Numerous repetitions of this experiment 
show that, although this sometimes 
occurs, in the majority of cases the 
extract will support neither germina¬ 
tion nor growth, even though heated 
for an hour in the steamer or auto¬ 
claved for one-half hour. Brown (2) 
reports that the inhibitory effect of 
the volatile substances arising from 
onion juice is greatly reduced or de¬ 
stroyed by boiling. 
It is to be expected that if the volatile 
onion oil consists of three compounds, 
as noted by Semmler (4), each with a 
different boiling point, the application 
of heat may remove or destroy certain 
of these more readily than others. 
Provided that they are all toxic, one 
would expect a gradual reduction in 
toxicity, depending on the temperature 
and the duration of heating. Two 
experiments on this phase of the prob¬ 
lem are reported. 
Experiment No. 1.—Juice of Yellow 
Globe onions was filtered and divided 
into four samples of 10 cc. each and a 
remainder which was kept for a con¬ 
trol. Two samples each were heated 
for varying periods in a water bath 
held at 70° and two at 96° C., respec¬ 
tively. To one tube in each bath a 
reflux condenser was attached to re¬ 
duce the loss of the volatile substances. 
One cubic centimeter samples were re¬ 
moved from each tube after 15, 30, 60, 
and 90 minutes. The samples thus 
obtained were tested by the usual 
method for the presence of volatile 
and dissolved toxins. 
The data given in Table II and repre¬ 
sented graphically in Figure 2 show that, 
on the whole, there is a gradual decrease 
in the amount of volatile toxin with 
continued heating and that the toxicity 
is reduced more rapidly at the higher 
temperatures. With the juices heated 
in open tubes there is a smooth curve 
produced, indicating a gradual loss in 
toxicity, but when the reflux condenser 
was attached there was a decided drop 
in both curves at 30 minutes, indicat¬ 
ing greater toxicity in juice thus heated 
than in that heated only 15 minutes. 
Obviously, an explanation of this fact 
will depend upon further analysis of 
the volatile substances and their reac¬ 
tion to temperature. 
The dissolved toxins were still suffi¬ 
ciently concentrated to kill any of the 
spores introduced directly into the ex¬ 
tract. 
Experiment No. 2. —Five cubic cen¬ 
timeters of onion juice was placed in a 
side-neck test tube and distilled over an 
open flame. About 1 c. c. of distillate was 
collected. The distillate and residue 
were then tested by the usual method 
for both dissolved and volatile toxins. 
(See Table III.) Although distillation 
was not continued for more than 5 
minutes, the heating seems to have had 
