MICHIGAN ACADEMY OF SCIENCE. 
199 
in the resistances of individual insects. This, however, appears not to he so 
serious as might be expected, although in every test one must use enough 
of them so that exceptional cases will not lead to erroneous conclusions. 
One peculiar instance of variability noted in the bed bugs and which may 
therefore be avoided when working for accurate results is that the young, 
light-colored or translucent insects are usually more resistant than the larger * 
full-fed ones. This is not invariably true but occurs so frequently as to be 
taken as a general rule. 
The rapidity with which bed bugs recover from immersions in dilutions 
of insecticides too great to be effective makes it possible to arrive at prompt 
conclusions; while its natural resistance makes it probable that conclusions 
drawn from results with this as the test insect will hold good for most others. 
Bv making one minute the invariable length of time the insect is submerged, 
the degree of dilution of the different insecticides may be used to determine 
the comparative efficiencies of such preparations. 
The effective working strengths however, may not have the same ratio 
because of the conditions surrounding the insect when in its natural location ; 
that each case has its peculiar conditions. A sheep's wool, for instance, will 
hold the material in contact with the insect much longer than can be hoped 
for when dipping swine. 
Having now a method of standardization which yields reasonably accurate 
results, it is possible to determine for any certain purpose what class of insecti- 
cides is most applicable. But the most valuable feature, is the opportunity 
it offers for working out new insecticides and determining at once what 
advantages they may possess over others; and also the possibility of deter- 
mining by further study how insecticides act, so that more intelligent means 
may be used for developing new preparations or improvements. 
Without any definite statement to that effect, the general proposition 
has been accepted that poisons, germicides, and insecticides belong -in the 
same catagory. But a glance at the accompanying chart and table shows 
a wide divergence in those values. 
A point brought out in the investigation of coal tar oils, and also graphic- 
ally shown in the chart, is that by proper manipulation one may obtain 
a product, the value of which is high, either as an insecticide or as a germicide 
and that the former property may be exceptionally high. 
We have confirmed the fact that the insecticidal value of soft soap is very 
considerable. This might raise the question whether the average coal tar 
dip on the market, the efficient dilution of which cannot in most cases be 
greater than 1 in 75, does not owe its efficiency to the soap contained. But 
more important than that is the question whether an oil is in the more effi- 
cient condition, in solution, or emulsified and in the form of globules of 
varying sizes. 
One would think without hesitation that a solution, or the very finest 
possible emulsion would be the more efficient because of being in the more 
penetrable form. Results with different oils, however, have not been suffi- 
ciently uniform to permit definite conclusions. Further work will be required 
with a greater range in the oils used and a greater diversity in t he conditions 
to decide this important point. The solution of this question is inseparably 
connected with the greater one, of how any contact insecticide performs it 
work. 
The coal tar insecticide and coal tar disinfectant mentioned in the list 
of products compared are made from different parts of the distillate from 
coal as obtained in the production of coke and gas. These redistilled por- 
