INFECTION EXPERIMENTS IN LABORATORY. 21 
fields not artifically treated would then show merely a spontaneous 
outbreak with a lower percentage of mortality. The settlement of 
these problems was merely a matter of experiment under conditions 
that would cover possibilities mentioned above. As soon as spring 
opened and weather permitted, field investigations began; the pur- 
pose being to ascertain whether artificial treatment of a field infested 
by chinch bugs would prove profitable. One phase of the matter 
as described earlier in this paper had already been settled; the 
Sporotrichum disease was widespread naturally over the infested sec- 
tion of the State. It remained to be shown, first, whether sowing 
fungus spores in an already infested field would increase the epidemic, 
and, second, in a field showing but little evidence of Sporotrichum 
whether such a treatment would start an epidemic, otherwise im- 
probable. 
Artificial Infection Experiments with Sporotrichum in the 
Laboratory. 
Preparatory to the field work it was found necessary to experiment 
with the fungus in the laboratory in order to determine the best 
method of propagation and the effect of the artificially grown cultures 
on chinch bugs. Quite definite results had already been obtained 
by Stevens, Barber, and Forbes, and advantage was taken of their 
conclusions, but at the same time it was thought best to experiment 
anew and adopt the methods best adapted to the experiments in hand. 
Sporotrichum was first isolated from transfers made into nutrient 
agar from a chinch bug dead of the disease. Once obtained pure, 
there was no difficulty in propagating it on artificial media. 
For field infection large quantities were needed, so that infection 
boxes which were designated for infecting bugs for distribution 
to farmers proved inadequate. The 10 c. m. petri dish used in 
bacteriological investigation was selected as the vessel in which to 
place the nutrient medium for growing the Sporotrichum. The fun- 
gus will grow on ordinary beef broth agar, but this was not found so 
useful as a combination of potato extract and corn meal. 
Virulence of artificial cultures. — It was realized early in the in- 
vestigation that the value of any work along lines of field infection 
depended upon a knowledge of the virulence of artificial cultures, 
since these were to be employed to a large extent. It was found that 
so much more fungus could be produced artificially with such cer- 
tainty that diseased bugs, while used, were not depended on for the 
major part of the work. To test the virulence of the fungus, experi- 
ments were conducted at various times by artificially infecting 
chinch bugs with culture fungus (that grown on the potato-cornmeal 
medium) and then comparing results with others not so infected or 
infected by the use of diseased bugs. 
