8 
a chemical change takes place in the Bayer compound, or, as seems more 
likely, the Karo merely ‘‘seals’’ the compound and allows it to retain its lethal 
properties. 
CONCLUSIONS 
Although the bait prepared from Karo syrup and Bayer L 13/59 gave 
unexpectedly good control of house flies over unexpectedly long periods of time, 
the hardened bait resulting from an undiluted syrup and a toxic substance 
should be regarded as the basis of only one of several techniques necessary to 
bring house fly populations to a desirably low level. The last fly or half 
dozen flies in a room are the hardest to kill with baits. Space sprays and 
repellents should be used in certain situations. Most important, sanitation, 
the elimination of places where flies breed, should be continued and intensi- 
fied. 
The Karo syrup with Bayer L 13/59, which proved relatively attractive 
to house flies in laboratory and field tests, might be improved by the addition 
of an attractant. Also, other syrups might prove more attractive and other 
poisons more effective against house flies without presenting any greater 
hazard to human beings. 
As of the date of this publication, the use of Bayer L 13/59 in a fly bait 
has not been passed upon by either the United States Food and Drug Adminis- 
tration or the Production and Marketing Administration. However, judged by 
the data now at hand, the toxicity of the bait recommended (1g grams of 
Bayer L 13/59 in 1 pint of Karo syrup) is such that 20 pints of it would approach 
the median lethal dose for a human being weighing 150 pounds. One pint of 
this bait (about 475 milliliters), sufficient for most premises, should present 
no toxicological hazards. 
Although the bait may be objectionable to some housewives who place 
an inordinately high value on neatness, it can with a small amount of ingenuity 
and artistic skill be so applied, even in homes, as to attract house flies without 
repelling finicky guests or members of the household. It is easily removed 
from wood or other smooth surfaces with a damp cloth, but, if objections are 
made to its being applied directly to parts of the house, it can be daubed on 
small pieces of paper or cardboard placed where flies alight. 
The hardened bait described above appears to offer a new and effective 
technique contributing to control of the house fly. 
