SOUTHERN CALIFORNIA ACADEMY OF SCIENCES 20 
Diseases of Scale Insects 
‘BY S. M. WOODBRIDGE, PH. D. 
There is nothing new or startling in the statement that the human 
race as well as other members of the animal kingdom have been subject 
to diseases and sometimes to epidemic diseases that have swept them 
eff by thousands and even millions. Among men the Black Death, 
Yellow Fever, are examples; among equines, glanders; among bovidia, 
anthrax and black leg; among porkers, cholera and in ‘the feathered 
kingdom gape and rupe may be mentioned. Vast sums of money have 
been spent and litrerly thousands of noble and brilliant men, the world 
over, have given their whole lives up to a study of these diseases and 
means of prevention. 
It is of comparatively recent date that bacteria have been proved 
to be the causes of disease, although as early as 1675 Antony van 
Leeuwenhoek, a Hollander, made discoveries which may be said to be 
the foundation-work for much that followed, and that has placed bac- 
teriology among the sciences; the trouble with van Leeuwenhoek’s work 
was that it didn’t stay discovered. 
It was not until a century later that ““Plerciz, a physician of Vienna, 
declared himself a firm believer in the work of van Leeuwenhoek, and 
based the Doctrine which he taught upon the discoveries of the Dutch 
observer, and upon observations of a confirmatory nature which he him- 
self had made. The doctrine of Plerciz assumed a casual relation be- 
tween the micro-organisms discovered and described by van Leeuwenhoek 
and all infectious. He claimed that the material of infection could be 
nothing else than a living substance and endeavored on these grounds 
to explain the variations in the period of incubation of the different dis- 
eases. He likewise believed the living contagium to be capable of mul- 
tiplication, within the body, and spoke of the possibility of its transmis- 
sion through the air. He claimed a special germ for each disease, 
holding that just as from a given cereal only one kind of grain can grow, 
so by the special germ for each disease only that disease can be pro- 
duced.”” (Abbott. ) 
The work and opinions of these scientists were ridiculed and no 
credence given them by the Medicos of their day. 
It was in the 4th and 5th decades of the last century that the true 
relation of the lower organisms to infectious diseases was scientifically 
pointed out by Pasteur, Davine and others. ‘The efforts of the bac- 
teriologists, and Medicos in the higher animal world, have been to isolate 
these diseases, cultivate these germs artificially in the laboratory, identify 
and classify them and discover means for their destruction, which at the 
same time, would not destroy the host upon which they were doing their 
deadly work. 
