Fuly 7, 1870] 
NATURE 
183 
to 1,000 or 1,500 for a single field of his microscope. He 
thén varied the mode of infection. He inoculated healthy 
worms with the corpusculous matter, and watched the 
consequent growth of the disease. He showed how the 
worms inoculate each other by the infliction of visible 
wounds with their “crochets.” In various cases he 
washed the “ crochets,” and found corpuscles in the water. 
He demonstrated the spread of infection by the simple 
association of healthy and diseased worms. In fact, the 
diseased worms sullied the leaves by their dejections, they 
also used their crochets, and spread infection in both ways. 
It was no hypothetical infected medium that killed the 
worms, but a definitely-organised and isolated thing. He 
examined the question of contagion at a distance, and 
demonstrated its existence. In fact, as might be expected 
from Pasteur’s antecedents, the investigation was exhaus- 
tive, the skill and beauty of his manipulation finding fitting 
correlatives in the strength and clearness of his thought. 
Pébrine was an enigma prior to the experiments of 
Pasteur. “Place,” he says, “the most skilful educator, 
even the most expert microscopist, in presence of large 
educations which present the symptoms described in our 
experiments ; his judgment will necessarily be erroneous if 
he confines himself to the knowledge which preceded 
my researches. The worms will not present to him the 
slightest spot of pébrine ; the microscope will not reveal 
the existence of corpuscles ; the mortality of the worms 
will be null or insignificant; and the cocoons leave 
nothing to be desired. Our observer would, therefore, 
conclude without hesitation that the eggs produced will 
be good forincubation. The truthis, on the contrary, that 
all the worms of these fine crops have been poisoned; 
that from the beginning they carried in them the germ of 
the malady ; ready to multiply itself beyond measure in 
the chrysalides and the moths, thence to pass into the 
eggs and smite with sterility the next generation. And 
what is the first cause of the evil concealed under so 
deceitful an exterior? In our experiments we can, so to 
speak, touch it with our fingers. It is entirely the effect 
of a single corpusculous repast ; an effect more or less 
prompt according to the epoch of life of the worm that 
has eaten the poisoned food.” 
It was work like this that I had in view when, in a 
lecture which has brought me much well-meant chas- 
tisement from a certain class of medical men, and much 
gratifying encouragement from a different clecs, I dwelt 
on the necessity of experiments of physical exactitude 
in testing medical theories. It is work like this 
which might be offered as a model to the physicians 
of England, many indeed of whom are pursuing with 
characteristic skill and energy the course marked out for 
them by this distinguished master. Prior to Pasteur, the 
most diverse and contradictory opinions were entertained 
as to the contagious character of pébrine ; some stoutly 
affirmed it, others as stoutly denied it. But on one point 
all were agreed. “They believed in the existence of a 
deleterious medium, rendered epidemic by some occult 
and mysterious influence, to which was attributed the 
cause of the malady.” Between such notions and the 
work of Pasteur, no physically-minded man will, I appre- 
hend, hesitate in his choice. 
Pasteur describes in detail his method of securing 
healthy eggs, which is nothing less than a mode of restor- 
ing to France her ancient prosperity in silk husbandry. 
And the justification of his work is to be found in the 
reports which reached him of the application, and the 
unparalleled success of his method, at the time he was 
putting his researches together for final publication. In 
France and Italy his method has been pursued with the 
most surprising results. It was an up-hill fight which led 
to this triumph, but it is consoling to think that even the 
stupidities of men may be converted into elements of growth 
and progress. Opposition stimulated Pasteur, and thus, 
without meaning it, did good service. “ Ever,” he says, 
“since the commencement of these researches, I have been 
exposed to the most obstinate and unjust contradictions ; 
but I have made it a duty to leave no trace of these con- 
tests in this book.” I have met with only a single allusion 
to the question of spontaneous generation in M. Pasteur’s 
work, In reference to the advantage of rearing worms 
in an isolated island like Corsica, he says :—“ Rien ne 
serait plus facile que d’éloigner, pour ainsi dire, d’une 
maniére absolue la maladie des corpuscles. Il est au 
pouvoir de l’homme de faire disparaitre de la surface du 
globe les maladies parasitaires, si, comme c'est ma convic- 
tion, la doctrine des générations spontanées est une 
chimére.” It is much to be desired that some really com- 
petent person in England should rescue the public mind 
from the confusion now prevalent regarding this question. 
M. Pasteur has investigated a second disease, called in 
France flacherie, which has co-existed with pébrine, but 
which is quite distinct from it. Enough, I trust, has been 
said to send the reader interested in these questions to 
the original volumes for further information. I report 
with deep regret the serious illness of M. Pasteur; an 
illness brought on by the labours of which I have tried 
to give some account. The letter which accompanied his 
volumes ends thus :—“ Permettez-moi de terminer ces 
quelques lignes que je dois dicter, vaincu que je suis par la 
maladie, en vous faisant observer que vous rendiez service 
aux Colonies de la Grande Bretagne en repandant la 
connaissance de ce livre, et des principes que j’ établis 
touchant la maladie des vers Asoie. Beaucoup de ces 
colonies pourraient cultiver le mirier avec succés, et en 
jetant les yeux sur mon ouvrage vous vous convaincrez 
aisement qu’il est facile aujourdhui, non seulement d’éloi- 
gner la maladie régnante, mais en outre de donner aux 
récoltes de la soie une prospérité qu’elles n’ont jamais eue.” 
Royal Institution, 30th June JOHN TYNDALL 
WHAT 1S ENERGY? 
III. 
THE CONSERVATION OF ENERGY 
jie is well-known that certain organisms of the animal 
world do not confine themselves to one state of being 
orto one order of existence, and the most familiar instance 
of this roving habit of life is the caterpillar, which passes 
first into the chrysalis state, and after that into the 
butterfly. This habit is not, however, peculiar to the 
organic world, for energy delights in similar transmuta- 
tions, and we have just seen how the eminently silent and 
invisible electrical current may occasionally be trans- 
muted into the vivid, instantaneous, awe-inspiring flash of 
lightning. Nor is this element of change confined to our 
peculiar corner of the universe, but it extends itself to 
