Sept. 15, 1870] 
window-pane, with a sort of magic circle, in white, drawn round 
them. On microscopic examination, the magic circle is found to 
consist of innumerable spores, which have been thrown off in all 
directions by a minute fungus called Zmpusa musce, the spore- 
forming filaments of which stand out like a pile of velvet from 
the body of the fly, These spore-forming filaments are con- 
nected with others which fill the interior of the fly’s body like so 
much fine wool, having eaten away and destroyed the creature’s 
viscera. This is the full-grown condition of the Ampusa. If 
traced back to its earlier stages, in flies which are still active, 
and to all appearance healthy, it is found to exist in the form of 
minute corpuscles which float in the blood of the fly. These 
multiply and lengthen into filaments, at the expense of the fly’s 
substance ; and when they have at last killed the patient, they 
grow out of its body and give off spores. Healthy flies shut up 
with diseased ones catch this mortal disease and perish like the 
others. A most competent observer, M. Cohn, who studied the 
development of the Z7pusa in the fly very carefully, was utterly 
unable to discover in what manner the smallest germs of the 
LEmpusa got into the fly. The spores could not be made to give 
rise to such germs by cultivation ; nor were such germs discover- 
able in the air, or in the food of the fly. It looked exceedingly 
like a case of Abiogenesis, or, at any rate, of Xenogenesis ; and 
it is only quite recently that the real course of events has been 
made out. It has been ascertained, that when one of the spores 
falls upon the body of a fly, it begins to germinate and sends out 
a process which bores its way through the fly’s skin ; this, having 
reached the interior cavities of its body, gives off the minute 
floating corpuscles which are the earliest stage of the Awpusa. 
The disease is ‘‘contagious,” because a healthy fly coming in 
contact with a diseased one, from which the spore-bearing fila- 
ments protrude, is pretty sure to carry off a spore or two. It is 
** infectious ” because the spores become scattered about all sorts 
of matter in the neighbourhood of the slain flies. 
The silkworm has long been known to be subject to a very 
fatal and infectious disease called the MJzuscardine. _Audouin 
transmitted it by inoculation. This disease is entirely due to the 
development of a fungus, Botrytis Bassiana, in the body of the 
caterpillar; and its contagiousness and infectiousness are accounted 
for in the same way as those of the fly-disease. But of late 
years a still more serious epizootic has appeared among the silk- 
worms ; and I may mention a few facts which will give you some 
conception of the gravity of the injury which it has inflicted on 
France alone. 
The production of silk has been for centuries an important 
branch of industry in Southern France, andin the year 1853 it 
had attained such a magnitude that the annual produce of the 
French sericulture was estimated to amount toa tenth of that of 
the whole world, and represented a money-value of 117,000,000 
of francs, or nearly five millions sterling. What may be the 
sum which would represent the money-value of all the industries 
connected with the working up of the raw silk thus produced is 
more than I can pretend to estimate. Suffice it to say that the 
city of Lyons is built upon French silk as much as Manchester 
was upon American cotton before the civil war. 
Silkworms are liable to many diseases; and even before 1853 
a peculiar epizootic, frequently accompanied by the appearance 
of dark spots upon the skin (whence the name of ‘‘ Pébrine” 
which it has received), had been noted for its mortality. But in 
the years following 1853 this malady broke out with such ex- 
treme violence, that, in 1858, the siik-crop was reduced toa 
third of the amount which it had reached in 1853; and, up till 
within the last year or two, it has never attained half the yield 
of 1853. This means not only that the great number of people 
engaged in silk growing are some thirty millions sterling poorer 
than they might have been ; it means not only that high prices 
have had to be paid for imported silkworm eggs, and that, after 
investing his money in them, in paying for mulberry-leayes and 
for attendance, the cultivator has constantly seen his silkworms 
perish and himself plunged in ruin ; but it means that the looms 
of Lyons haye lacked employment, and that for years enforced 
idleness and misery have been the portion of a vast population 
which, in former days, was industrious and well to do. 
In 1858 the gravity of the situation caused the French Academy 
of Sciences to appoint Commissioners, of whom a distinguished 
naturalist, M. de Quatrefages, was one, to inquire into the nature of 
this disease, and, if possible, to devise some means of staying the 
plague. In reading the Report* made by M. de Quatrefages in 
1859, it is exceedingly interesting to observe that his elaborate 
* Etudes sur les Maladies Actuelles des Vers & Sole, p. 53. 
NATURE 
403 
study of the Pébrine forced the conviction upon his mind that, 
in its mode of occurrence and propagation, the disease of the 
silkworm is, in every respect, comparable to the cholera among 
mankind, But it differs from the cholera, and so far is a more 
formidable disease, in being hereditary, and in being, under 
some circumstances, contagious as well as infectious. 
The Italian naturalist; Filippi, discovered in the blood of the 
silkworms affected by this strange disease a multitude of cylin- 
drical corpuscles, each about gg Of an inch long. These have 
been carefully studied by Lebert, and named by him Pazz/isto- 
Piyton ; for the reason that in subjects in which the disease is 
strongly developed, the corpuscles swarm in every tissue and 
organ of the body, and even pass into the undeveloped eggs of 
the female moth. But are these corpuscles causes, or mere con- 
comitants, of the disease? Some naturalists took one view and 
some another ; andit was not until the French Government, 
alarmed by the continued ravages of the malady, and the in- 
efficiency of the remedies which had been suggested, dispatched 
M. Pasteur to study it, that the question received its final settle- 
ment ; at a great sacrifice, not only of the time and peace of 
mind of that eminent philosopher, but, I regret to have to add, 
of his health.* 
But the sacrifice has not been in vain. It is now certain that 
this devastating, cholera-like Pébrine is the effect of the growth 
and multiplication of the Panhistophyton in the silkworm. It is 
contagious and infectious because the corpuscles of the Pamhisto- 
Phyton pass away from the bodies of the diseased caterpillars, 
directly or indirectly, to the alimentary canal of healthy silk- 
worms in their neighbourhood ; it is hereditary, because the 
corpuscles enter into the eggs while they are being formed, and 
consequently are carried within them when they are laid ; and for 
this reason, also, it presents the very singular peculiarity of 
being inherited only on the mother’s side. There is not a 
single one of all the apparently capricious and unaccountable 
phenomena presented by the Pébrine, but has received its ex- 
planation from the fact that the disease is the result of the 
presence of the microscopic organism, Pavhistophyton. 
Such being the facts with respect to the Pébrine, what are the 
indications as to the method of preventing it? It is obvious 
that this depends upon the way in which the~Pavhistophyton is 
generated. If itmay be generated by Abiogenesis, or by Xeno- 
genesis, within the silkworm orits moth, the extirpation of the 
disease must depend upon the prevention of the occurrence of 
the conditions under which this generation takes place. But if, 
on the other hand, the Fan/istophyton is an independent organism, 
which isno more generated by the silkworm than the mistletoe 
is generated by the oak or the apple-tree on which it grows, 
though it may need the silkworm for its development in the 
same way as the mistletoe needs the tree, then the indications 
are totally different. The sole thing "to be done is to get rid of 
and keep away the germs of the Pamhistophyton. As wight be 
imagined, from the course of his previous investigations, M, 
Pasteur was led to believe that the latter was the right theory ; 
and, guided by that theory, he has devised a method of extir- 
pating the disease, which has proved to be completely successful 
wherever it has been properly carried out. 
There can be no reason, then, for doubting that, among 
insects, contagious and infectious diseases, of great malignity, 
are caused by minute organisms which are produced from pre- 
existing germs, or by homogenesis ; and there is no reason, that 
I know of, for believing that what happens in insects may not 
take place in the highest animals. Indeed, there is already 
strong evidence that some diseases of an extremely malignant and 
fatal character to which man is subject, are as much the work of 
minute organisms as is the Pébrine. I refer for this evidence 
to the very striking facts adduced by Professor Lister in his 
various well-known publications on the antiseptic method of 
treatment. It seems to me impossible to rise from the perusal 
of those publications without a strong conviction that the lament: 
able mortality which so frequently dogs the footsteps of the most 
skilful operator, and those deadly consequences of wounds and 
injuries which seem to haunt the very walls of great hospitals, 
and are, even now, destroying more men than die of bullet or 
bayonet, are due to the importation of minute organisms into 
wounds, and their increase and multiplication; and that the 
surgeon who saves most lives will be he who best works out the 
practical consequences of the hypothesis of Redi, 
* In NaTuRE, No.xxxvi., p. 181, will be found a résumé, by Prof, Tyndall, 
of Pasteur’s investigations of the silkworm disease,—Ep, 
