NATURE 
181 
THURSDAY, JULY 7, 1870 
PASTEUR’S RESEARCHES ON THE DISEASES 
OF SILKWORMS 
HAVE recently received from M. Pasteur a copy of 
his new work, “Sur la Maladie des vers a soie,” a 
notice of which, however brief and incomplete, will, I am 
persuaded, interest a large class of the readers of NATURE. 
The book is the record of a very remarkable piece of 
scientific work, which has been attended with very re- 
markable practical results. For fifteen years a plague 
had raged among the silkworms of France. They had 
sickened and died in multitudes, while those that suc- 
ceeded in spinning their cocoons furnished only a fraction 
of the normal quantity of silk. In 1853 the silk culture of 
France produced a revenue of one hundred and thirty 
millions of francs. During the twenty previous years the 
revenue had doubled itself, and no doubt was entertained 
as to its future augmentation. “ Unhappily, at the moment 
when the plantations were most flourishing, the prosperity 
was annihilated by a terrible scourge.” The weight of 
the cocoons produced in France in 1853 was twenty-six 
millions of kilogrammes ; in 1865 it had fallen to four 
millions, the fall entailing in the single year last men- 
tioned a loss of one hundred millions of francs. 
The country chiefly smitten by this calamity happened 
to be that of the celebrated chemist Dumas, now per- 
petual secretary of the French Academy of Sciences. 
He turned to his friend, colleague, and pupil, Pasteur, 
and besought him with an earnestness which the circum- 
stances rendered almost personal, to undertake the investi- 
gation of the malady. Pasteur at this time had never 
seen a silkworm, and he urged his inexperience in reply 
to his friend. But Dumas knew too well the qualities 
needed for such an inquiry to accept Pasteur’s reason for 
declining it. “Je met,” said he, “un prix extréme a voir 
votre attention fixée sur la question qui interesse mon 
pauvre pays ; la mis¢re surpasse tout ce que vous pouvez 
imaginer.” Pamphlets about the plague had been showered 
upon the public, the monotony of waste paper being broken 
at rare intervals by a more or less useful publication. 
“The Pharmacopeeia of the Silkworm,” wrote M. Cor- 
nalia in 1860, “is now as complicated as that of man. 
Gases, liquids, and solids have been laid under contribu- 
tion. From chlorine to sulphurous acid, from nitric acid 
to rum, from sugar to sulphate of quinine,—all has been 
invoked in behalf of this unhappy insect.” The helpless 
cultivators, moreover, welcomed with ready trustfulness 
every new remedy, if only pressed upon them with suffi- 
cient hardihood. It seemed impossible to diminish their 
blind confidence in their blind guides. In 1863 the French 
Minister of Agriculture himself signed an agreement to 
pay 500,000 francs for the use of a remedy which its pro- 
moter declared to be infallible. It was tried in twelve 
different departments of France and found perfectly useless. 
In no single instance was it successful. It was under 
these circumstances that M. Pasteur, yielding to the 
entreaties of his friend, betook himself to Alais in the 
beginning of June 1865. As regards silk husbandry, 
this was the most important department in France, and 
it was also that which had been most sorely smitten by 
the epidemic, 
VOL, II. 
-diseased eggs. 
The silkworm had been previously attacked by mscar- 
dine ; a disease proved by Bassi to be caused by a vegetable 
parasite. Muscardine, though not hereditary, was propa- 
gated annually by the parasitic spores, which, wafted by 
winds, often sowed the disease in places far removed from 
the centre of infection. According to Pasteur, muscardine 
is now very rare ; but for the last fifteen or twenty years 
a deadlier malady has taken its place. A frequent out- 
ward sign of this disease are the black spots which cover 
the silkworms, hence the name pébrine, first applied to 
the plague by M. de Quatrefages, and adopted by Pasteur. 
Pébrine also declares itself in the stunted and unequal 
growth of the worms, in the languor of their movements, 
in their fastidiousness as regards food, and in their prema- 
ture death. The discovery of the inner workings of the 
epidemic may be thus traced. In 1849 Guerin Méne- 
ville noticed in the blood of certain silkworms vibratory 
corpuscles which he supposed to be endowed with inde- 
pendent life, and to which he gave a distinctive name. As 
regards the motion of the particles, Filippi proved him 
wrong ; their motion was the well-known Brownian motion. 
But Filippi himself committed the error of supposing the 
corpuscles to be normal to the life of the insect. They 
are really the cause of its mortality—the form and sub- 
stance of itsdisease. This was studied and well described 
by Cornalia ; while Lebert and Frey subsequently found 
the corpuscles not only in the blood, but in all the tissues 
of the silkworm. Osimo, in 1857, discovered the corpuscles 
in the eggs, and on this observation Vittadiani founded, in 
1859, a practical method of distinguishing healthy from 
The test often proved fallacious, and it 
was never extensively applied. 
The number of these corpuscles is sometimes enormous. 
They take possession of the intestinal canal, and spread 
thence throughout the body of the worm. They fill the 
silk cavities, the stricken insect often going through the 
motions of spinning without any material to answer to the 
act. Its organs, instead of being filled with the clear 
viscous liquid of the silk, are packed to distension by these 
corpuscles. On this feature of the plague Pasteur fixed 
his attention. He pursued it with the skill which apper- 
tains to his genius, and with the thoroughness that 
belongs to his character. The cycle of the silkworm’s 
life is briefly this :— From the fertile egs comes the little 
worm, which grows, and after some time casts its skin. 
This process of moulting is repeated two or three times 
at subsequent intervals during the life of the insect. 
After the last moulting the worm climbs the brambles 
placed to receive it, and spins among themits cocoon. It 
passes thus into a chrysalis; the chrysalis becomes a 
moth, and the moth when liberated lays the eggs which 
form the starting-point of a new cycle. Now Pasteur 
proved that the plague-corpuscles might be incipient in 
the egg, and escape detection ; they might also be ger- 
minal in the worm, and still baffle the microscope. But 
as the worm grows, the corpuscles grow also, becoming 
larger and more defined. In the aged chrysalis they are 
more pronounced than in the worm; while in the moth, 
if either the egg or the worm from which it comes should 
have been at all stricken, the corpuscles infallibly appear, 
offering no difficulty of detection. This was the first great 
point made out in 1865 by Pasteur. The Italian naturalists, 
as aforesaid, recommended the examination of the eggs 
L 
