Scientific American Supplement, No. 595, May 28, 1887 online

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consider, also, that hospital wards are occupied day and night, and
continuously for weeks, it is not to be wondered at that microbes are
abundant therein.

I want especially to dwell upon the fact that foci, and probably
productive foci, may exist outside the body. It is highly probable,
judging from the results of experiments, that every collection of
putrescible matter is potentially a productive focus of microbes. The
thought, of a pit or sewer filled with excremental matters mixed with
water, seething and bubbling in its dark warm atmosphere, and
communicating directly (with or without the intervention of that
treacherous machine called a trap) with a house, is enough to make one
shudder, and the long bills of mortality already chargeable to this
arrangement tell us that if we shudder we do not do so without cause. As
an instance of the way in which dangers may work in unsuspected ways, I
may mention the fact that Emmerich, in examining the soil beneath a ward
of a hospital at Amberg, discovered therein the peculiar bacillus which
causes pneumonia, and which had probably been the cause of an outbreak of
pneumonia that had occurred in that very ward.

The importance of "Dutch cleanliness" in our houses, and the abolition of
all collections of putrescible matter in and around our houses, is
abundantly evident.

It will not be without profit to examine some well-known facts, by the
aids of the additional light which has been thrown upon them by the study
of the microbes which are in the media around us.

There is no better known cause of a high death rate than overcrowding.
Overcrowding increases the death rate from infectious diseases,
especially such as whooping cough, measles, scarlet fever, diphtheria,
small-pox, and typhus. The infection of all these diseases is
communicable through the air, and where there is overcrowding, the chance
of being infected by infective particles, given off by the breath or
skin, is of course very great. Where there is overcrowding, the
collections of putrescible filth are multiplied, and with them probably
the productive foci of infective particles. Tubercular disease, common
sore throat, chicken-pox, and mumps, are also among the diseases which
are increased by overcrowding.

To come to details which are more specific, let us consider the case of
some diseases which are definitely caused by floating matter in the air.
First, let us take one which is apparently attributable to pollen.


Among diseases which are undoubtedly caused by floating matter in the air
must be reckoned the well-known malady "hay fever," which is a veritable
scourge during the summer months to a certain percentage of persons, who
have, probably, a peculiarly sensitive organization to begin with, and
are, in a scientific sense, "irritable."

This disease has been most thoroughly and laboriously investigated by Mr.
Charles Blackley, of Manchester, who, being himself a martyr to hay
fever, spent ten years in investigating the subject, and published the
result in 1873, in a small work entitled "Experimental Researches on the
Causes and Nature of _Catarrhus aestivus_ (hay fever or hay asthma)."

Mr. Blackley had little difficulty in determining that the cause of his
trouble was the pollen of grasses and flowers, and his investigations
showed that the pollen of some plants was far more irritating than the
pollen of others. The pollen of rye, for example, produced very severe
symptoms of catarrh and asthma, when inhaled by the nose or mouth. Mr.
Blackley came to the conclusion that the action of the pollen was partly
chemical and partly mechanical, and that the full effect was not produced
until the outer envelope burst and allowed of the escape of the granular

Having satisfied himself that pollen was capable of producing all the
symptoms of hay fever, Mr. Blackley next sought to determine, by a series
of experiments, the quantity of pollen found floating in the atmosphere
during the prevalence of hay fever, and its relation to the intensity of
the symptoms. The amount of pollen was determined by exposing slips of
glass, each having an area of a square centimeter, and coated with a
sticky mixture of glycerine, water, proof spirit, and a little carbolic
acid. Mr. Blackley gives two tables, showing the average number of pollen
grains collected in twenty-four hours on one square of glass, between May
28 and August 21, in both a rural and an urban position. The maximum both
in town and country was reached on June 28, when in the town 105 pollen
grains were deposited, and in the country 880 grains. The number of
grains deposited was found to vary much, falling almost to zero during
heavy rain and rising to a maximum if the rain were followed by bright
sunshine. Mr. Blackley found that the severity of his own symptoms
closely corresponded to the number of pollen grains deposited on his
glasses. Mr. Blackley devised some very ingenious experiments to
determine the number of grains floating in the air at different
altitudes. The experiments were conducted by means of a kite, to which
the slips of glass were attached, fixed in an ingenious apparatus, by
means of which the surface of the glass was kept covered until a
considerable altitude had been reached. Mr. Blackley's first experiment
gave as a result that 104 pollen grains were deposited in the glass
attached to the kite, while only 10 were deposited on a glass near the
ground. This experiment was repeated. Again and again, and always with
the same result, there was more pollen in the upper strata of the air
than in the lower.

A very interesting experiment was performed at Filey, in June, 1870. A
breeze was blowing from the sea, and had been blowing for 12 or 15
hours. Mr. Blackley flew his kite to an elevation of 1,000 feet. The
glass attached to the kite was exposed for three hours, and on it there
were 80 grains of pollen, whereas a similar glass, exposed at the margin
of the water, showed no pollen nor any organic form. Whence came this
pollen collected on the upper glass? Probably from Holland or Denmark.
Possibly from some point nearer the center of Europe.


A study of the terrible disease which so often attacks the potato crop in
this country will serve, I think, to bring forcibly before you certain
untoward conditions which may be called climatic, and which are
attributable to fungoid spores in the air.

With the potato disease you are all, probably, more or less practically
acquainted. When summer is at its height, and when the gardeners and
farmers are all looking anxiously to the progress of their crops, how
often have we heard the congratulatory remark of "How well and strong
those potatoes look!" Such a remark is most common at the end of July or
the beginning of August, when the green part, or haulm, of the plant is
looking its best, and when the rows of potatoes, with their elegant rich
foliage and bunches of blossom, have an appearance which would almost
merit their admission to the flower border. The same evening, it may be,
there comes a prolonged thunder storm, followed by a period of hot,
close, moist, muggy weather. Four-and-twenty hours later, the hapless
gardener notices that certain of his potato plants have dark spots upon
some of their leaves. This, he knows too well, is the "plague spot," and
if he examine his plants carefully, he will perhaps find that there is
scarcely a plant which is not spotted. If the thunder shower which we
have imagined be followed by a long period of drought, the plague may be
stayed and the potatoes saved; but if the damp weather continue, the
number of spotted leaves among the potatoes increases day by day, until
the spotted leaves are the majority; and then the haulm dies, gets slimy,
and emits a characteristic odor; and it will be found that the tubers
beneath the soil are but half developed, and impregnated with the disease
to an extent which destroys their value.

Now, the essential cause of the potato disease is perfectly well
understood. It is parasitical, the parasite being a fungus, the
_Peronospora infestans_, which grows at the expense of the leaves, stems,
and tubers of the plant until it destroys their vitality. If a diseased
potato leaf be examined with the naked eye, it will be seen that, on the
upper surface, there is an irregular brownish black spot, and if the
under surface of the leaf be looked at carefully, the brown spot is also
visible, but it will be seen to be covered with a very faint white bloom,
due to the growth of the fungus from the microscopic openings or
"stomata," which exist in large numbers on the under surface of most
green leaves. The microscope shows this "bloom" to be due to the
protrusion of the fungus in the manner stated, and on the free ends of
the minute branches are developed tiny egg shaped vessels, called
"conidia," in which are developed countless "spores," each one of which
is theoretically capable of infecting neighboring plants.

Now, it is right to say that, with respect to the mode of spread of the
disease, scientific men are not quite agreed. All admit that it may be
conveyed by contact, that one leaf may infect its neighbors, and that
birds, flies, rabbits, and other ground game may carry the disease from
one plant to another and from one crop to another. This is insufficient
to account for the sudden onset and the wide extent of potato
"epidemics," which usually attack whole districts at "one fell swoop."
Some of those best qualified to judge believe that the spores are carried
through the air, and I am myself inclined to trust in the opinion
expressed by Mr. William Carruthers, F.R.S., before the select committee
on the potato crop, in 1880. Mr. Carruthers' great scientific
attainments, and his position as the head of the botanical department of
the British Museum, and as the consulting naturalist of the Royal
Agricultural Society, at least demand that his opinion should be received
with the greatest respect and consideration. Mr. Carruthers said (report
on the potato crop, presented to the House of Commons, July 9, 1880,
question 143 _et seq._): "The disease, I believe, did not exist at all in
Europe before 1844.... Many diseases had been observed; many injuries to
potatoes had been observed and carefully described before 1844; but this
particular disease had not. It is due to a species of plant, and although
that species is small, it is as easily separated from allied plants as
species of flowering plants can be separated from each other. This plant
was known in South America before it made its appearance in this country.
It has been traced from South America to North America, and to Australia,
and it made its first appearance in Europe in Belgium, in 1844, and
within a very few days after it appeared in Belgium, it was noticed in
the Isle of Wight, and then within almost a few hours after that it
spread over the whole of the south of England and over Scotland.... When
the disease begins to make its appearance, the fungus produces these
large oblong bodies (_conidia_), and the question is how these bodies are
spread, and the disease scattered.... I believe that these bodies, which
are produced in immense quantities, and very speedily, within a few hours
after the disease attacks the potato, are floating in the atmosphere, and
are easily transplanted by the wind all over the country. I believe this
is the explanation of the spread of the disease in 1844, when it made its
appearance in Belgium. The spores produced in myriads were brought over
in the wind, and first attacked the potato crops in the Isle of Wight,
and then spread over the south of England. The course of the disease is
clearly traced from the south of England toward the midland counties, and
all over the island, and into Scotland and Ireland. It was a progress
northward.... This plant, the _Peronospora infestans_, will only grow on
the _Solanum tuberosum_, that is, the cultivated potato.... Just as
plants of higher organization choose their soils, some growing in the
water and some on land, so the _Peronospora infestans_ chooses its host
plant; and its soil is this species, the _Solatium tuberosum_. It will
not grow if it falls on the leaves of the oak or the beech, or on grass,
because that is not its soil, so to speak. Now, the process of growth is
simply this: When the conidia fall on the leaf, they remain there
perfectly innocent and harmless unless they get a supply of water to
enable them to germinate.... The disease makes its appearance in the end
of July or the beginning of August, when we have, generally, very hot
weather. The temperature of the atmosphere is very high, and we have
heavy showers of rain."

The warmth and moisture are, in fact, the conditions necessary for the
germination of the conidia. Their contents (zoospores) are liberated, and
quickly grow in the leaf, and soon permeate every tissue of the plant.

It was clearly established before the committee that not all potatoes
were equally liable to the disease. The liability depends upon strength
of constitution. It is well known that potatoes are usually, almost
invariably, propagated by "sets," that is, by planting tubers, or
portions of tubers, and this method of propagation is analogous to the
propagation of other forms of plants by means of "cuttings." When
potatoes are raised from seed, it is found that some of the "seedlings"
present a strength of constitution which enables them to resist the
disease for some years, even though the subsequent propagation of the
seedling is entirely from "sets." The raising of seedling potatoes is a
tedious process, but the patience of the grower is often rewarded by
success, and I may allude to the fact that the so-called "Champion
potato," raised from seed in the first instance by Mr. Nicoll, in
Forfarshire, and since propagated all over the country, has enjoyed,
deservedly as it would appear, a great reputation as a disease-resisting
potato; but all who have a practical knowledge of potato growing seem
agreed that we cannot expect its disease-resisting quality to last at
most more than twenty years from its first introduction (in 1877), and
that in time the constitution of the "Champion" will deteriorate, and it
will become a prey to disease.

There is some evidence to show, also, that the constitution of the potato
may be materially influenced by good or bad culture. Damp soils,
insufficient or badly selected manures, the selection of ill developed
potatoes for seed, and the overcrowding of the "sets" in the soil, all
seem to act as causes which predispose the potatoes to the attacks of the
parasite. Strong potatoes resist disease, just as strong children will;
while weak potatoes, equally with weak children, are liable to succumb to
epidemic influences.

The following account of some exact experiments carried out by Mr. George
Murray, of the Botanical Department of the British Museum, seems to show
that Mr. Carruthers' theory as to the diffusion of conidia through the
air is something more than a speculation:

"In the middle of August, 1876," says Mr. Murray, "I instituted the
following experiments, with the object of determining the mode of
diffusion of the conidia of _Peronospora infestans_.

"The method of procedure was to expose on the lee side of a field of
potatoes, of which only about two per cent, were diseased, ordinary
microscopic slides, measuring two inches long by one inch broad, coated
on the exposed surface with a thin layer of glycerine, to which objects
alighting would adhere, and in which, if of the nature of conidia, they
would be preserved. These slides were placed on the projecting stones of
a dry stone wall which surrounded the field, and was at least five yards
from the nearest potato plant. During the five days and nights of the
experiment, a gentle wind blew, and the weather was, on the whole, dry
and clear. Every morning, about nine o'clock, I placed fourteen slides on
the lee side of the field, and every evening, about seven o'clock, I
removed them, and placed others till the following morning at nine
o'clock. The fourteen slides exposed during the day, when examined in the
evening, showed (among other objects):

On the first day. 15 conidia.
" second day. 17 "
" third day. 27 "
" fourth day. 4 "
" fifth day. 9 "

"On none of the five nights did a single conidium alight on the slides.
This seemed to me to prove that during the day the conidia, through the
dryness of the atmosphere and the shaking of the leaves, became detatched
and wafted by the air; while during the night the moisture (in the form
of dew, and on one occasion of a slight and gently falling shower)
prevented the drying of the conidia, and thus rendered them less easy of

"I determined the nature of the conidia (1) by comparing them with
authentic conidia directly removed from diseased plants; (2) by there
being attached to some of them portions of the characteristic
conidiaphores; and (3) by cultivating them in a moist chamber, the result
of which was, that five conidia, not having been immersed in the
glycerine, retained their vitality, which they showed by bursting and
producing zoospores in the manner characteristic of _Peronospora


Let us look at another disease by the light of recent knowledge, viz.,
the epidemic influenza, concerning which I remember hearing much talk, as
a child, in 1847-48. There has been no epidemic of this disease in the
British Isles since 1847, but we may judge of its serious nature from the
computation of Peacock that in London alone 250,000 persons were stricken
down with it in the space of a few days. It is characteristic of this
disease that it invades a whole city, or even a whole country, at "one
fell swoop," resembling in its sudden onset and its extent the potato
disease which we have been considering.

The mode of its spreading forbids us to attribute it, at least in any
material degree, although it may be partially so, to contagion in the
ordinary sense, i.e., contagion passing from person to person along the
lines of human intercourse. It forbids us also to look at community of
water supply or food, or the peculiarities of soil, for the source of the
disease virus. We look, naturally, to some atmospheric condition for the
explanation. That the atmosphere is the source of the virus is made more
likely from the fact that the disease has broken out on board ship in a
remarkable way. In 1782, there was an epidemic, and on May 2 in that
year, says Sir Thomas Watson -

"Admiral Kempenfelt sailed from Spithead with a squadron, of which the
Goliah was one. The crew of that vessel were attacked with influenza on
May 29, and the rest were at different times affected; and so many of the
men were rendered incapable of duty by this prevailing sickness, that the
whole squadron was obliged to return into port about the second week in
June, not having had communication with any port, but having cruised
solely between Brest and the Lizard. In the beginning of the same month
another large squadron sailed, all in perfect health, under Lord Howe's
command, for the Dutch coast. Toward the end of the month, just at the
time, therefore, when the Goliah became full of the disease, it appeared
in the Rippon, the Princess Amelia, and other ships of the last mentioned
fleet, although there had been no intercourse with the land."

Similar events were noticed during the epidemic of 1833:

"On April 3, 1833, the very day on which I saw the first two cases that I
did see of influenza - all London being smitten with it on that and the
following day - the Stag was coming up the Channel, and arrived at two
o'clock off Berry Head on the coast of Devonshire, all on board being at
that time well. In half an hour afterward, the breeze being easterly and
blowing off the land, 40 men were down with the influenza, by six o'clock
the number was increased to 60, and by two o'clock the next day to 160.
On the self-same evening a regiment on duty at Portsmouth was in a
perfectly healthy state, but by the next morning so many of the soldiers
of the regiment were affected by the influenza that the garrison duty
could not be performed by it."

After reviewing the various hypotheses which had been put forward to
account for the disease, sudden thaws, fogs, particular winds, swarms of
insects, electrical conditions, ozone, Sir Thomas Watson goes on to say:

"Another hypothesis, more fanciful perhaps at first sight than these, yet
quite as easily accommodated to the known facts of the distemper,
attributes it to the presence of innumerable minute substances, endowed
with vegetable or with animal life, and developed in unusual abundance
under specific states of the atmosphere in which they float, and by which
they are carried hither and thither."

This hypothesis has certainly more facts in support of it now than it had
when Sir Thomas Watson gave utterance to it in 1837. And when another
epidemic of influenza occurs, we may look with some confidence to having
the hypothesis either refuted or confirmed by those engaged in the
systematic study of atmospheric bacteria. Among curious facts in
connection with influenza, quoted by Watson, is the following: "During
the raging of one epidemic, 300 women engaged in coal dredging at
Newcastle, and wading all day in the sea, escaped the complaint." Reading
this, the mind naturally turns to Dr. Blackley's glass slide exposed on
the shore at Filey, and upon which no pollen was deposited, while eighty
pollen grains were deposited on a glass at a higher elevation.


Let us next inquire into the evidence regarding the conveyence of
small-pox through the air. In the supplement to the Tenth Report of the
Local Government Board for 1880-81 (c. 3,290) is a report by Mr. W.H.
Power on the influence of the Fulham, Hospital (for small-pox) on the
neighborhood surrounding it. Mr. Power investigated the incidence of
small-pox on the neighborhood, both before and after the establishment of
the hospital. He found that, in the year included between March, 1876,
and March, 1877, before the establishment of the hospital, the incidence
of small-pox on houses in Chelsea, Fulham and Kensington amounted to 0.41
per cent. (i.e., that one house out of every 244 was attacked by
small-pox in the ordinary way), and that the area inclosed by a circle
having a radius of one mile round the spot where the hospital was
subsequently established (called in the report the "special area") was,
as a matter of fact, rather more free from small-pox than the rest of the
district. After the establishment of the hospital in March, 1877, the
amount of small-pox in the "special area" round the hospital very notably
increased, as is shown by the table by Mr. Power, given below.

This table shows conclusively that the houses nearest the hospital were
in the greatest danger of small-pox. It might naturally be supposed that
the excessive incidence of the disease upon the houses nearest to the
hospital was due to business traffic between the hospital and the
dwellers in the neighborhood, and Mr. Power admits that he started on his
investigation with this belief, but with the prosecution of his work he
found such a theory untenable.


+ - - - -+ - - - - - - - - - - -+ - - - - - - - - - - - - - - - - - - - - - - - - +
| | Incidence on every 100 houses within the |
| | special area and its divisions. |
Cases of|The epidemic periods + - - - - + - - - - -+ - - - - -+ - - - - -+ - - - - -+
acute |since opening |On total|On small |On first |On second|On third |
small- |of hospital. |special | circle, | ring, | ring, | ring, |
pox. | | area. |0-¼ mile.|¼-½ mile.|½-¾ mile.|¾-1 mile.|
- - - - + - - - - - - - - - - -+ - - - - + - - - - -+ - - - - -+ - - - - -+ - - - - -+
327 |March-December 1877 | 1.10 | 3.47 | 1.37 | 1.27 | 0.36 |
714 |January- | | | | | |
| September, 1878 | 1.80 | 4.62 | 2.55 | 1.84 | 0.67 |
679 |September 1878- | | | | | |
| October 1879 | 1.68 | 4.40 | 2.63 | 1.49 | 0.64 |
292 |October, 1879- | | | | | |

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Online LibraryVariousScientific American Supplement, No. 595, May 28, 1887 → online text (page 6 of 10)