71 
come in emit act a\ ith each other, and then for a brief time only. There- 
fore, should a Boll Worm become diseased upon either com or cotton, 
the natural conditions and habits of the past are such thatthe chances 
for infecting- other individuals through it arc reduced to a minimum. 
This also explains the failure of the disease of Pieris rapce and Plusia 
brassicce to attack the Boll Worm, and spreading to it through the nat- 
ural processes of infection and dissemination. On this point, however, 
another consideration must be noted in the case of Pieris rapce. From 
the observations already recorded for this disease, it is found that, 
though present, it developed rather tardily in its host under the pre- 
vailing conditions. In addition, it appears to be less virulent and ap- 
parently has less power of contagion, since it does not seem to infest 
others of its own species so readily as in more northern districts, such 
as Illinois, Indiana, and Iowa. This seems to be due mostly to the dif- 
ferences in climatic conditions, the atmosphere being drier, much higher 
in temperature, and the hot summer season much more protracted in the 
South. The well-known devitalizing effect of hot, scorching sun-light 
under high temperatures upon many bacteriological organisms seems 
therefore to explain the lesser virulence of this germ in the locality 
where the investigation was prosecuted. Accordingly, the Pieris dis- 
ease is unpromising at present as an agent in destroying the Boll Worm 
in that section. The germ is doubtless becoming more acclimated and 
adapting itself to prevailing conditions, so that it may be expected to 
become more efficient in that region in the future. 
For the Plusia disease, however, the high temperature seems to be a 
necessary factor, and, so far as the writer's information goes, is less 
virulent in the cooler or northern districts. 
Experiment 1, in which a pure culture of the boll-worm germ obtained 
by artificial culture methods wasted to healthy Boll Worms, tailed 
again to produce the disease. The same genu was ted to larvae oi 
Pieris rapce as detailed in experiments 2 and -'5. In experiment 2, 50 
per cent died. In experiment 3, all died. Subsequent studies of the 
dead pupse in these two experiments, as also the records of the checks 
upon them, together with microscopic examinations, proved that death 
could not be attributed to the boll-worm germ with any degree of cer- 
tainty. On the contrary, death seems to have been due to their own 
specific germs, as noted in the experiment. Reversing the trial, the 
germ of Pieris was used in experiment I. ami ted to the Boll Worms 
without producing disease. The Plusia germ was then led to Pieris 
larvae as in experiment 6, and to Boll Worms as in experiment 7, with- 
out bringing about diseased conditions. Furthermore, Pieris larvae, 
feeding upon the same plants and leaves along with diseased Plusias, 
did so w ith perfect immunity . 
What does it all mean 1 It is unsafe to hazard any positive state- 
ments and the discussion must be understood as being provisional. 
Granting that the germs in question are trulj parasitic upon then re 
