Fan. 27, 1870] 
focus of the electric beam and inhale the dirt revealed there. 
Nor is the disgust abolished by the reflection that, although we 
do not see the nastiness, we are churning it in our lungs every 
hour and minute of our lives. There is no respite to this con- 
tact with dirt; and the wonder is, not that we should from time 
to time suffer from its presence, but that so small a portion of it 
would appear to be deadly to man. 
And what is this portion? It was some time ago the current 
belief that epidemic diseases generally were propagated by a kind 
of malaria, which consisted of organic matter in a state of o/o7- 
decay; that when such matter was taken into the body through the 
lungs or skin, it had the power of spreading there the destroying 
process which had attacked itself. Such a spreading power was 
visibly exerted in the case of yeast. A Jittle leaven was seen to 
leaven the whole lump, a mere speck of matter in this supposed 
state of decomposition being apparently competent to propagate 
indefinitely its own decay. Why should not a bit of rotten malaria 
work in a similar manner within the human frame? In 1836 very 
wonderful reply was given to this question. In that year Cagniard 
de la Tour discovered the yeast plant, a living organism, which 
when placed in a proper medium, feeds, grows, and reproduces 
itself, and in this way carries on the process which we name 
fermentation. Fermentation was thus proved to be a product 
of life instead of a process of decay. 
Schwann, of Berlin, discovered the yeast plant independently, 
and in February 1837 he also announced the important result, 
that when a decoction of meat is effectually screened from 
ordinary air, and supplied solely with air which has been 
raised to a high temperature, putrefaction never sets in. Putre- 
faction, therefore, he affirmed to be caused by something derived 
from the air, which something could be destroyed by a suffi- 
ciently high temperature. The experiments of Schwann were 
repeated and confirmed by Helmholtz and Ure. But as regards 
fermentation, the minds of chemists, influenced probably by 
the great authority of Gay-Lussac, who ascribed putrefaction 
to the action of oxygen, fell back upon the old notion of 
matter in a state of decay. It was not the living yeast plant, 
but the dead or dying parts of it, which, assailed by oxygen, 
produced the fermentation. ‘This notion was finally exploded 
by Pasteur. He proved that the so-called “ferments” are not 
such ; that the true ferments are organised beings which find 
in the reputed ferments their necessary food. 
Side by side with these researches and discoveries, and 
fortified by them and others, has run the germ theory of 
epidemic disease. The notion was expressed by Kircher, and 
favoured by Linnzeus, that epidemic diseases are due to germs 
which float in the atmosphere, enter the body, and produce 
disturbance by the development within the body of parasitic 
life. While it was still struggling against great odds, this 
theory found an expounder and a defender in the President of 
this Institution. Ata time when most of his medical brethren 
considered it a wild dream, Sir Henry Holland contended 
that some form of the germ theory was probably true. The 
strength of this theory consists in the perfect parallelism of the 
phenomena of contagious disease with those of life. As a 
planted acorn gives birth to an oak competent to produce a 
whole crop of acorns, each gifted with the power of reproducing 
its parent tree, and as thus from a single seedling a whole 
forest may spring, so these epidemic diseases literally plant 
their seeds, grow, and shake abroad new germs, which, meeting 
in the human body their proper food and temperature, finally 
take possession of whole populations. Thus Asiatic cholera, 
beginning in a small way in the Delta of the Ganges, contrived 
in seventeen years to spread itself over nearly the whole habit- 
alle world. The development from an infinitesimal speck of 
the virus of small-pox of a crop of pustules, each charged with 
the original poison, is another illustration. The reappearance 
of the scourge, as in the case of the Dreadnought at Greenwich, 
reported on so ably by Dr. Budd and Mr. Busk, receives a satis- 
factory explanation from the theory which ascribes it to the lin- 
gering of germs about the infected place. 
Surgeons have long known the danger of permitting air to 
enter an open abscess. To prevent its entrance they employ a 
tube called a cannula, to which is attached a sharp steel point 
called a trocar. They puncture with the steel point, and by 
gentle pressure they force the pus through the cannula. It is 
necessary to be very careful in cleansing the instrument ; and it 
is difficult to see how it can be cleansed by ordinary methods in 
air loaded with organic impurities, as we have proved our air to 
be. The instrument ought, in fact, to be made as hot as its 
NEA TA FUE, 
341 
temper will bear. But this is not done, and hence, notwithstand- 
ing all the surgeon’s care, inflammation often sets in after the 
first operation, rendering necessary a second and a third. Rapid 
putrefaction is found to accompany this new inflammation. The 
pus, moreover, which was sweet at first, and showed no trace of 
animal life, is now fetid, and swarming with active little organisms 
called vibrios. Prof. Lister, from whose recent lecture this fact 
is derived, contends, with every show of reason, that this rapid 
putrefaction and this astounding development of animal life are 
due to the entry of germs into the abscess during the first opera- 
tion, and their subsequent nurture and development under favour- 
able conditions of food and temperature. The celebrated 
physiologist and physicist Helmholtz is attacked annually by 
hay-fever. From the 20th of May to the end of June he suffers 
from a catarrh of the upper air-passages ; and he has found 
during this period, and at no other, that his nasal secretions are 
peopled by these vibrios. They appear to nestle by preference 
in the cavities and recesses of the nose, for a strong sneeze is 
necessary to dislodge them. 
These statements sound uncomfortable; but by disclosing 
our enemy they enable us to fight him. When he clearly eyes 
his quarry the eagle’s strength is doubled, and his swoop is 
rendered sure. If the germ theory be proved true, it will 
give a definiteness to our efforts to stamp out disease which 
they could not previously possess. And it is only by definite 
effort under its guidance that its truth or falsehood can be 
established. It is difficult for an outsider like myself to read 
without sympathetic emotion such papers as those of Dr. Budd, 
of Bristol, on cholera, scarlet-fever, and small-pox. He is a 
man of strong imagination, and may occasionally take a flight 
beyond his facts; but without this dynamic heat of heart, the 
stolid inertia of the free-born Briton cannot be overcome. 
And as long as the heat is employed to warm up the truth 
without singeing it over-much ; as long as this enthusiasm can 
overmatch its mistakes by unequivocal examples of success, so 
long am I disposed to give it a fair field to work in, and to 
wish it God speed. 
But let us return to our dust. It is needless to remark that 
it cannot be blown away by an ordinary bellows; or, more 
correctly, the place of the particles blown away is in this case 
supplied by others ejected from the bellows, so that the track 
of the beam remains unimpaired. But if the nozzle of a good 
bellows be filled with cotton wool not too tightly packed, the 
air urged through the wool is filtered of its floating matter, 
and it then forms a clean band of darkness in the illuminated 
dust. This was the filter used by Schroéder in his experi- 
ments on spontaneous generation, and turned subsequently to 
account in the excellent researches of Pasteur. Since 1868 
I have constantly employed it myself. 
But by far the most interesting and important illustration 
of this filtering process is furnished by the human breath. 
I fill my lungs with ordinary air and breathe through a glass 
tube across the electric beam. The condensation of the 
aqueous vapour of the breath is shown by the formation of a 
luminous white cloud of delicate texture. It is necessary to 
abolish this cloud, and this may be done by drying the 
breath previous to its entering into the beam; or still 
more simply, by warming the glass tube. When this is done the 
luminous track of the beam is for a time uninterrupted. The 
breath impresses upon the floating matter a transverse motion, 
but the dust from the lungs makes good the particles displaced. 
But after some time an obscure disc appears upon the beam, the 
darkness of which increases, until finally, towards the end of the 
expiration, the beam is, as it were, pierced by an intensely black 
hole, in which no particles whatever can be discerned. The air, 
in fact, has so lodged its dirt within the lungs as to render the 
last portions of the expired breath absolutely free from suspended 
matter. This experiment may be repeated any number of times 
with the same result. It renders the distribution of the dirt 
within the lungs as manifest as if the chest were transparent. 
I now empty my lungs as perfectly as possible, and placing a 
handful of cotton wool against my mouth and nostrils, inhale 
through it. There is no difficulty in thus filling the lungs with 
air. On expiring this air through the glass tube, its freedom from 
floating matter is at once manifest. From the very beginning of 
the act of expiration the beam is pierced bya black aperture. 
The first puff from the lungs abolishes the illuminated dust and 
puts a patch of darkness in its place, and the darkness continues 
throughout the entire course of the expiration. When the tube 
is placed below the beam and moved to and fro, the same 
