Oct. i6 ,1916 
Effects of Nicotine as an Insecticide 
99 
paralysis. Since paralysis is an affection of the nervous system, it still 
remains to be shown that nicotine applied as an insecticide reaches the 
nervous system and how it affects the nerve cells. The following pages 
deal with this portion of the work. Many difficulties were encountered, 
and the experiments performed to determine how nicotine affects the 
nerve cells gave no definite answer to this question. The latter phase of 
this subject is presented mostly by giving a brief discussion of the various 
views pertaining to the physical and chemical effects of drugs on cells. 
Tracing the nicotine into the various insect tissues was accomplished 
by precipitating this alkaloid immediately after it had killed the insects 
and then by carefully studying the microscopical sections made from the 
insects thus tested. A study of this nature involves considerable tech¬ 
nique and many precautions in making sections, because two objects 
instead of one must be successfully accomplished at the same time. It 
is an easy matter to obtain good sections of most larvae and soft-bodied 
insects under ordinary conditions, but it was found quite difficult to 
obtain good sections and at the same time not to lose the precipitates 
held in the tissues while the slides were being run through the various 
reagents. This is appreciated when we consider the solubility of various 
substances in the clearing oils, in the alcohols, and in water. 
In addition to the difficulties enumerated above, there are still three 
more to be considered: (1) After a certain period has elapsed following 
death as a result of having been treated with nicotine, the tissues of the 
insects were unusually abnormal upon fixation. As soon as life is ex¬ 
tinct, and probably a short time before, the cells gradually change from 
normal to abnormal ones. This was particularly noticeable when small 
caterpillars were sprayed with solutions of nicotine. A short time 
after death they turned brown and the tissues were found to be more or 
less disintegrated. For this reason it was always necessary to fix the 
insects just before the last signs of life had disappeared in order to avoid 
mistaking post-mortem changes in the cells for physical ones caused by 
the nicotine. (2) On the other hand, if nicotine really causes physical 
changes in the cells of insects, these changes are always masked by the 
large physical ones caused by the fixing reagents. (3) It is often difficult 
and sometimes impossible to distinguish the precipitated insecticide in¬ 
side the tissues from the coagulated constituents of the cells caused by 
the fixative. Fischer (8) regards the coagulation of these constituents, 
which really constitutes fixation, as a true precipitation, but of course 
it is a milder form. The coagulated particles are, nevertheless, frequently 
as large and sometimes larger than the precipitated ones. 
I.—TRACING COLORED LIQUIDS INTO INSECTS 
Before determining whether or not nicotine spray solutions as applied 
under practical conditions reach the tissues by passing through the 
spiracles, many preliminary experiments were performed to ascertain 
