19 
The bacterial diseases of insects attack first the cellular lining 
of the alimentary canal and afterwards penetrate to the blood. 
Disturbance of the digestive functions is thus the primary diffi¬ 
culty, and the final result is a very rapid post-mortem decay of 
all the fluids and tissues, the body speedily becoming a filthy 
semi-fluid mass. 
THE BEGINNINGS OF KNOWLEDGE AND THE PROGRESS OF 
INVESTIGATION. 
Contagious insect diseases have been vaguely known for many 
centuries those of the domestic insects, bees and silkworms, first 
and most precisely. Aristotle’s observation that the honey-bee is 
subject to diseases (History of Animals, VIII., 26) probably had 
reference to one or both of those now called dysentery and foul- 
brood, both contagious and both due to bacterial infection. To¬ 
wards the close of the seventeenth century the contagious 
maladies of the silkworm so ravaged the hatcheries of France 
that despairing silk growers were only prevented from destroying 
their mulberry plantations by official orders to the contrary, and 
twice at least in the following century a like calamity fell upon 
them. 
The various silkworm diseases were not at first discriminated; 
but muscardiue was intelligibly described in 1763, was known as 
contagious in 1819, as characterized by a fungous efflorescence in 
1820, and as capable of transfer to caterpillars of other species in 
1829. Its fungus was studied botanically and described as a 
Botrytis in 1835, transferred by inoculation to other silkworms in 
1836, and found spontaneous among wild insects of different 
orders in 1839. By these discoveries the foundation was laid thus 
early for an economic method applicable to the destruction of 
injurious species by infection with spores of the fungus of naus¬ 
ea rdine. 
The first species of Entomophthora recognized was the common 
house-fly fungus, E. muscce , described in 1829. 
Foul-brood of bees was called by that name at least as early as 
1767, but the first bacterial insect disease distinctly recognized as 
such (in 1858) was flacherie or schlafsucht of the silkworm, con¬ 
clusively studied by Pasteur in 1868, and by Ferry de la Bellone 
and others in 1876 to 1879. 
The first of the plant parasites of less familiar insects to at¬ 
tract attention were those which produce a conspicuous rod-like 
or club-shaped growth from the body after death, and many ob- 
servatioos on these peculiar growths were published during the 
eighteenth century. The common club-fungus (Cordyceps) of our 
American white grub is an example. 
Parasitism of silkworms by Protozoa (Sporozoa), causing what 
is perhaps the most destructive of all contagious insect diseases 
(. p&brine ) was recognized by Leydig in 1857. Balbiani’s studies of 
the life history of this parasite in 1866 and 1867 and Pasteur’s 
practical researches in 1867 and 1868 put our knowledge of this 
disease also on a firm foundation. 
