102 PSYCHE [October 
from caterpillars the preceding year. In addition, the tree was very carefully pro- 
tected from any foreign caterpillars or insects, and was carefully watered like the 
other trees used in the experiments. ‘The food was regularly renewed each morning 
and evening, and the caterpillars themselves were sprayed one morning in each week 
with ordinary tap water just before they were given fresh food. 
From the foregoing results I have therefore been led to believe that the artifi- 
cially produced flacherie can be utilized as a valuable aid in the destruction of Gypsy 
Moth caterpillars. As is well known, the disease commonly appears in nature only 
after the caterpillars are full grown, and even then only during unusually dry or very 
damp seasons. ‘The fact that I have now succeeded in rendering the caterpillars 
susceptible to flacherie before the third molt (Experiment 1.) may be of importance 
for the practical use of the disease, since by artificially inducing flacherie, relief might 
be had weeks sooner than happens in nature. In addition to this my experiments 
admit of the conclusion reached by Suzuki who experimented on mulberry trees in 
Japan. (Cf. “Zeitschrift f. Planzenkrankheiten,” XII. Band, Jahrg. 1902, 4. Heft 
p. 203-226, 5 Heft p. 258-278.) Suzuki found that in the case of insufficient nourish- 
ment there was also a concomitant increase in the acidity of the leaves (p. 272). 
If this be the case, it would seem that the alkaline reaction of the digestive juices 
must be neutralized in order to bring on the first susceptibility of the disease. Full 
grown caterpillars are most readily affected because at each stage of their growth the 
alkalinity of their digestive fluid decreases. Normal young caterpillars have a strongly 
alkaline fluid, which, according to the researches of Verson and Bolle, has the power 
to destroy the “polyhedric corpuscles” which are very resistant to disinfectants 
(Fischer, p. 542). That the alkalinity of the digestive juices of the young caterpillars 
actually suffers a decrease through insufficient nourishment is indicated by my 
experiments, since in these cases the young caterpillars succumbed to the disease. 
Had the alkaline content of the digestive juices not decreased, the pathogenic or- 
ganisms should not have shown increased virulence. 
In addition to the five experiments previously described, a sixth one was under- 
taken in an open field containing a group of oak and another of willow trees each of 
which was infested with about five thousand caterpillars. Upon each of these two 
groups of trees one hundred sick caterpillars and fifty dead ones were distributed. 
The larvee were ready for the fourth molt at the beginning of the experiment, and 
even on the next day the count of dead specimens could be begun. The disease — 
spread with amazing rapidity till by the time of pupation about four thousand cater- | 
pillars on each group of trees had succumbed. Two conditions, which did not enter 
into my previous experiments, united to cause this unusual result. In the first place, 
