CHAPTER I. 
INTRODUCTION 
EARLY SUGGESTIONS REGARDING THE TRANSMISSION OF DISEASE 
BY INSECTS 
Until very recent years insects and their allies have been considered 
as of economic importance merely in so far as they are an annoyance 
or direct menace to man, or his flocks and herds, or are injurious to 
his crops. It is only within the past fifteen years that there has 
sprung into prominence the knowledge that in another and much more 
insiduous manner, they may be the enemy of mankind, that they 
may be among the most important of the disseminators of disease. 
In this brief period, such knowledge has completely revolutionized 
our methods of control of certain diseases, and has become an import¬ 
ant weapon in the fight for the conservation of health. 
It is nowhere truer than in the case under consideration that how¬ 
ever abrupt may be their coming into prominence, great move¬ 
ments and great discoveries do not arise suddenly. Centuries ago 
there was suggested the possibility that insects were concerned with 
the spread of disease, and from time to time there have appeared keen 
suggestions and logical hypotheses along this line, that lead us to 
marvel that the establishment of the truths should have been so long 
delayed. 
One of the earliest of these references is by the Italian physician, 
Mercurialis, who lived from 1530 to 1607, during a period when 
Europe was being ravaged by the dread “black death”, or plague. 
Concerning its transmission he wrote: “There can be no doubt that 
flies feed on the internal secretions of the diseased and dying, then, 
flying away, they deposit their excretions on the food in neighboring 
dwellings, and persons who eat of it are thus infected.” 
It would be difficult to formulate more clearly this aspect of the 
facts as we know them to-day, though it must always be borne in 
mind that we are prone to interpret such statements in the light of 
present-day knowledge. Mercurialis had no conception of the animate 
nature of contagion, and his statement was little more than a lucky 
guess. 
Much more worthy of consideration is the approval which was 
given to his view by the German Jesuit, Athanasius Kircher in 1658. 
