NATURE 
[Fuly-7, 1870 
before risking their incubation. Pasteur showed that 
both eggs and worms might b2 smitten and still pass 
muster, the culture of such eggs or such worms being sure 
to entail disaster. He made the moth his starting-point 
in seeking to regenerate the race. 
And here is to be noted a point of immense practical 
importance. The worms issuing from the eggs of perfectly 
healthy moths may afterwards becom: themselves  in- 
fected through contact with diseased worms, or through 
germs mixed with the dust of the rooms in which the 
worms are fed. But though the moths derived from the 
worms thus infected may be so charged with corpuscles 
as to be totally unable to produce egzs fit for incuba- 
tion, still Pasteur shows that the worms themselves, in 
which the disease is not hereditary, never perish before 
spinning their cocoons. This, as I have said, is a point 
of capital importance; because it shows that the moth- 
test, if acted upon, even though the worms during their 
“education” should contract infection, secures, at all 
events, the next subsequent crop. 
Pasteur made his first communication on this subject 
to the Academy of Sciences in September 1$55. It raised 
a cloud of criticism. Here forsooth was a chemist 
rashly quitting his proper m¢/er and presuming to lay 
down the law for the physician and biologist on a sub- 
ject which was eminently theirs. “On trouva étrange que 
je fusse si peu au courant dela question ; on m’ opposa 
des travaux qui avaient paru depuis longtemps en Italie, 
dont les resultats montraient linutilité de mes efforts, et 
Vimpossibilité d’arriver 4 un resultat pratique dans la 
direction que je m’étais engagé. Que mon ignorance fut 
grande au sujet des recherches sans nombre qui avaient 
paru depuis quinze années.” Pasteur heard the buzz, but he 
continued his work. In choosing the eggs intended for 
incubation, the cultivators selected those produced in the 
successful “educations” of the year. But they could not 
understand the frequent and often disastrous failures of 
their selected eggs ; for they did not know, and nobody 
prior to Pasteur was competent to tell them, that the 
finest cocoons may envelop doomed corpusculous moths. 
It was not, however, easy to’ make the cultivators accept 
new guidance. To strike their imagination and if possible 
determine their practice, Pasteur hit upon the expedient 
of prophecy. In 1865 he inspected at St. Hippolyte-du- 
Fort fourteen different parcels of eggs intended for incu- 
bation. Having examined a sufficient number of the 
moths which produced these eggs, he wrote out the predic- 
tion of what would occur in 1867, and placed the pro- 
phecy as a sealed letter in the hands of the Mayor of St. 
Hippolyte. 
In 1867 the cultivators communicated to the mayor 
their results. The letter of Pasteur was then opened 
and read, and it was found that in twelve out of fourteen 
cases, there was absolute conformity between his pre- 
diction and the observed facts. Many of the educa- 
tions had perished totally; the others had perished 
almost totally; and this was the prediction of Pasteur, 
In two out of the fourteen cases, instead of the pro- 
phesied destruction, half an average crop was obtained, 
Now, the parcels of eggs here referred to were considered 
healthy by their owners. They had been hatched and 
tended in the firm hope that the labour expended on 
them would prove remunerative. The application of the 
moth-test for a few minutes in 1866 would have saved the 
labour and averted the disappointment. Two additional 
parcels of eggs were at the same time submitted to Pas- 
teur. He pronounced them healthy ; and his words were 
verified by the production of an excellent crop. Other 
cases of prophecy still more remarkable, because more 
circumstantial, are recorded in the work before us, 
These deadly corpuscles were found by Leydig in 
other insects than the silkworm moth. He considers 
them to belong to the class of psososperms founded by J. 
Miiller. ‘‘ This,” says Pasteur, “is to regard the corpus- 
cular organism as a kind of parasite, which propagates itself 
after the manner of parasites of its class.” Pasteur sub- 
jected the development of the corpuscles to a searching 
examination. With admirable skill and completeness he 
also examined the various modes by which the plague is 
propagated. He obtained perfectly healthy worms from 
moths perfectly free from corpuscles, and selecting from 
them 10, 20, 30, 50, as the case might be, he introduced 
into the worms the corpusculous matter. It was first 
permitted to accompany the food. Let us take a single 
example out of many. Rubbing up a small corpusculous 
worm in water, he smeared the mixture over the mul- 
berry leaves. Assuring himself that the leaves had been 
eaten, he watched the consequences from day today. Side 
by side with the infected worms he reared their fellows, 
keeping them as much as possible out of the way of 
infection. These constituted his “lot temoign,” his 
standard of comparison. On the 16th of April, 1868, he 
thus infected thirty worms. Up to the 23rd they re- 
mained quite well. On the 25th they seemed well, but 
on that day corpuscles were found in the intestines of two 
of the worms subjected to microscopic examination. The 
corpuscles begin to be formed in the tunic of the intestine. 
On the 27th, or eleven days after the infected repast, two 
fresh worms were examined, and not only was the intes- 
tinal canal found in each case invaded, but the silk organ 
itself was found charged with the corpuscles. On the 
28th the twenty-six remaining worms were covered by the 
black spots of pébrine. On the 30th the difference of 
size between the infected and non-infected worms was very 
striking, the sick worms being not more than two-thirds ot 
the size of the healthy ones. On the 2nd of May a worm 
which had just finished its fourth moulting was examined. 
Its whole body was so filled with corpuscles as to excite 
astonishment that it could live. The disease advanced, 
the worms died and were examined, and on the 11th of 
May only six out of the thirty remained. They were the 
strongest of the lot, but on being searched they also were 
found charged with corpuscles. Not one of the thirty 
worms had escaped; a single corpusculous meal had 
poisoned them all. The standard lot, on the contrary, 
spun their fine cocoons, and two only of their moths were 
found to contain any trace of corpuscles. These had doubt- 
less been introduced during the rearing of the worms. 
As his acquaintance with the subject increased, Pasteur’s 
desire for precision augmented, and he finally gives the 
growing number of corpuscles seen in the field of his 
microscope from day to day. After a contagious repast 
the number of worms containing the parasite gradually 
augmented until finally it became cent. per cent. The 
number of corpuscles would at the same time rise 
from o to 1, to Io, to roo, and sometimes even 
