2 
Introduction 
One cannot read carefully his works without believing that long 
before Leeuwenhook’s discovery, Kircher had seen the larger species of 
bacteria. Moreover, he attributed the production of disease to these 
organisms and formulated, vaguely, to be sure, a theory of the animate 
nature of contagion. It has taken two and a half centuries to 
accumulate the facts to prove his hypothesis. 
The theory of Mercurialis was not wholly lost sight of, for in the 
medical literature of the eighteenth century there are scattered 
references to flies as carriers of disease. Such a view seems even to 
have been more or less popularly accepted, in some cases. Gudger 
(1910), has pointed out that, as far back as 1769, Edward Bancroft, 
in “An Essay on the Natural History of Guiana in South America,” 
wrote concerning the contagious skin-disease known as “Yaws”: 
“It is usually believed that this disorder is communicated by the flies 
who have been feasting on a diseased object, to those persons who have 
sores, or scratches, which are uncovered; and from many observa¬ 
tions, I think this is not improbable, as none ever receive this disorder 
whose skins are whole.” 
Approaching more closely the present epoch, we find that in 1848, 
Dr. Josiah Nott, of Mobile, Alabama, published a remarkable 
article on the cause of yellow fever, in which he presented “reasons for 
supposing its specific cause to exist in some form of insect life.” 
As a matter of fact, the bearing of Nott’s work on present day ideas 
of the insect transmission of disease has been very curiously overrated. 
The common interpretation of his theory has been deduced from a few 
isolated sentences, but his argument appears quite differently when 
the entire article is studied. It must be remembered that he wrote at 
a period before the epoch-making discoveries of Pasteur and before 
the recognition of micro-organisms as factors in the cause of disease. 
His article is a masterly refutation of the theory of “malarial” origin 
of “all the fevers of hot climates,” but he uses the term “insect” as 
applicable to the lower forms of life, and specific references to “mos¬ 
quitoes,” “aphids,” “cotton-worms,” and others, are merely in the 
way of similes. 
But, while Nott’s ideas regarding the relation of insects to yellow 
fever were vague and indefinite, it was almost contemporaneously 
that the French physician, Louis Daniel Beauperthuy argued in the 
most explicit possible manner, that yellow fever and various others 
are transmitted by mosquitoes. In the light of the data which were 
available when he wrote, in 1853, it is not surprising that he erred by 
