ON THE POISONS OF PLANT-LICE.* 
By J. Dewirz, 
Metz, Germany. 
Although applied entomology has made enormous progress 
during recent years both in its scope and importance, we cannot 
deny that it has hitherto moved only in certain restricted paths 
and is therefore in danger of becoming one-sided, for the subject 
is taken up at present almost exclusively with a study of life- 
histories, with parasites and the empirically ascertained methods 
of combatting injurious species.; Thus it has come about 
that up to the present time we know very little concerning 
the secretion of poisons by the sucking plant-parasites and the 
effects of these poisons on the plants. Most attention has been 
paid to this question by those who have investigated the origin 
of plant galls. Hence it may be of interest to record some 
investigations which I have made on the poisons of plant-lice. 
In addition to the bacterial poisons we may distinguish 
those of certain animals (snakes, scorpions, bees, etc.) which 
are characterized only by certain pecularities such as the lack 
of an incubation period. These animal poisons have been best 
studied in snakes. But there are also some researches on the 
poisons of arthropods (spiders, myriopods, insects). The 
attempt, however, has hardly been made to investigate care- 
fully the poisons produced by the plant parasites, especially 
by the plant lice. 
The toxins of bacteria and fungi and the animal poisons 
have the property of hamolyzing, or dissolving the red pigment 
(hemoglobin) of the blood corpuscles of mammals, and we 
therefore speak of the haemolysis of the toxins and of animal 
poisons. Under their influence a dilution of red blood corpuscles 
in physiological salt solution takes on a clear, transparent, 
red color like that of lac. The poison of a particular species, 
however, will haemolyze only the red blood-corpuscles of par- 
ticular species of mammals, namely, those which are susceptible 
to the poison in question; the red blood-corpuscles of other 
*Translation by W. M. Wheeler. 
tJ. Dewitz, Die Physiologie in der Schadlingsforschung. Trans. Second Ent. 
Congress 1912 pp. 234-244; The Bearing of Physiology on Economic Entomology. 
Bull. Ent. Research, Vol. 3, 1912, pp. 343-354. 
343 
