Such diseases have seldom or never visited the shores of temperate
countries, or at least have obtained no lasting foothold there, even
when the conditions have been favorable to them. Among such diseases
are Yellow Fever, Sleeping Sickness (which must not be confused with
the so-called ‘Sleepy Sickness’), Beri-Beri, Dengue, Sprue, Kalar-azar,
and a host of other less known conditions.
It must be said, to avoid misunderstanding, that ‘the Tropics’ in the
medical sense is a region considerably wider and far less well-defined
than the geographical Tropics. Moreover, despite the existence of
diseases peculiar to the Tropics, ‘tropical diseases’ form no natural
group based on any common organic causation. The organisms that give
rise to the various ‘tropical diseases’ differ from one another just
as much as the organisms that give rise to the diseases of temperate
countries.
Since we cannot speak of tropical diseases on the basis of their
common causation, we are forced to deal with them as separate entities
and especially from the point of view of their prevention. We will
therefore select two diseases, the history of which illustrates the
process by which the Tropics have been rendered safer both for European
and for native races. These will serve as types, and we will choose
one from the truly tropical group which does not invade temperate
climes, and the other from the group which is being gradually excluded
from temperate climes. No better instances of these two groups can be
adduced than Yellow Fever and Malaria.
[Illustration:
FIG. 120. A common Malaria-carrying mosquito × 3.
FIG. 121. The Yellow Fever-carrying mosquito × 3.]
(a) _Yellow Fever._
In discussing the history of Yellow Fever, as of many other conditions,
it is perhaps best to begin at the end, for modern knowledge of the
organic cause of a disease often illumines and gives a meaning to
historical records.
In 1918 the Japanese investigator Noguchi observed a very delicate
and minute spiral organism in the blood of a case of Yellow Fever at
Guayaquil, the principal port of Ecuador, on the West Coast of South
America, one of the most important endemic centers of the disease.
Noguchi showed that guinea-pigs inoculated with the blood of this
infected case developed symptoms similar to those of Yellow Fever, and
he was able to demonstrate the same organism in the sick guinea-pigs.
He passed the disease by means of inoculation from one guinea-pig
to another. He succeeded in obtaining pure cultures of the organism
on artificial media. He passed such cultures through a series of
guinea-pigs and finally recovered it in pure culture again. He showed
that different strains vary greatly in virulence, a fact in accord with
the great variability in the gravity of attacks of Yellow Fever.
One of the reasons why the discovery of this organism has been so long
delayed is doubtless the very small numbers in the blood of patients
suffering from Yellow Fever. Thus, the toxins must be extremely
powerful. Indeed, it has been shown that 1/10,000 of a cubic centimeter
of a virulent culture rapidly induces fatal symptoms in a guinea-pig.
There are other important points about the Yellow Fever organism. It
passes through a stage in which it is so small as to be beyond the
reach even of microscopic vision. This fact is known because the blood
of a Yellow Fever patient is infective when passed through any but
the finest filters. The organism in fact exists in what is called a
‘Filter-Passing’ stage. Of late years a number of infective diseases
have been shown to be due to filter-passing organisms of this type.
Among them is the organism of the disease known as Infantile Paralysis
(p. 270). The study of ‘filter-passers’ bids fair to be in itself a
special science.
Finally, Noguchi threw light on the nature of Yellow Fever epidemics.
He was able to pass the parasite from one guinea-pig to another, not
only by inoculation in the ordinary way, but also by means of the bite
of a species of mosquito which has long been known to be the carrier
of the disease for man. He showed that a period of some twelve days’
duration within the body of the insect is necessary for the parasite
again to develop its dangerous phase. The period of incubation in
man, that is, the time that passes between the infective insect bite
and the appearance of the disease, is 3-5 days, but 12-14 days is the
period that usually elapses after the introduction of a case of the
disease before other cases occur. The discrepancy is now explained.
The disease is not infectious except through the mosquito, so the
developmental period of the parasite within the mosquito corresponds to
the incubation period of the epidemic.
Outbreaks of Yellow Fever have struck the public imagination, have
given rise to folk tales and have inspired poets. The story of the
_Flying Dutchman_ is that of a ship stricken with Yellow Fever. The
specter ship is supposed by sailors to haunt the seas around the Cape
of Good Hope, and to bode ill for those who see it. A murder was
committed on the ship, and following it ‘Yellow Jack’ broke out. All
ports were closed to the wretched crew, who finally all died of the
disease. The _Flying Dutchman_ was the subject of an opera by Wagner
and a novel by Marryat. A picture of a ship smitten by Yellow Jack is
to be found in Coleridge’s _Ancient Mariner_.
An historic case may be quoted. In 1837 a barque named _Huskisson_ was
at Sierra Leone. She was lading when Yellow Fever appeared among the
crew. All but two or three died. Yellow Fever broke out in the colony,
but gradually died down. The _Huskisson_, in the meantime, remained in
harbor without hands for three months. At last, hands were obtained,
tempted by very high pay. Again the Yellow Fever broke out among them
and again nearly all died. They were bitten by infected mosquitoes
which remained in the ship during the three months. Many cases, no
less dramatic, are on record. The disease is among those which are
peculiarly common and fatal among medical men. Thus, Senegal has twice
been denuded of medical men by Yellow Fever. In 1830 six died out of
twelve, and in 1878 twenty-two out of twenty-seven.
An attack of Yellow Fever confers Immunity. In children it assumes a
mild form, and therefore, in countries where the disease is endemic,
the population consists largely of the survivors of attacks. On this
account terrible outbreaks of the _Flying Dutchman_ or _Ancient
Mariner_ type are always either on immigrant ships or in places which
have remained long unvisited by the disease, in other words such
outbreaks occur under conditions in which immune persons are few or
absent.
The distribution of the Yellow Fever mosquito is wider than the
distribution of Yellow Fever at the present day, but Yellow Fever is
never found, save in sporadic outbreaks, where the mosquito cannot live
permanently. The distribution of the mosquito corresponds, however,
to the areas where the disease has in the past, from time to time,
established itself, but is smaller than the area wherein sporadic
outbreaks have been reported.
During the seventeenth and eighteenth and even the nineteenth century
there were repeated outbreaks of Yellow Fever far beyond the region to
which it is now confined. Along the eastern shores of North America it
has at times extended as far north as New York, and there have been
destructive outbreaks in Baltimore, Philadelphia, and even Boston. The
disease has been found along most of the littoral of South America. In
the Old World it has visited chiefly West Africa, where it was imported
very early by the slave trade. It has visited at times Spain, Portugal,
and Italy with devastating epidemics, and has even occasionally made a
call in France and once in England. The last considerable outbreak in
Europe was at Madrid in 1878.
England has always had important interests in the West Indies. During
the eighteenth and first half of the nineteenth century she had,
moreover, large military establishments there, which were regarded as
very bad stations. In Thackeray’s _Vanity Fair_, which refers to the
period just after the Napoleonic wars, the disreputable and unfortunate
Rawdon Crawley is sent as governor to ‘Coventry Island’ in the West
Indies, and is not expected to last long! There are many historic
occasions on which the British forces in the West Indies lost almost
incredible numbers from Yellow Jack, garrisons being practically wiped
out. In Jamaica the mean annual mortality in the garrison was for many
years 185 per 1,000! In the Bermudas the mortality was about 80 per
1,000. One should remember that soldiers are picked men in the prime of
life, and that these mortality rates were in places now regarded as
health resorts! A hundred years ago, Jamaica had the highest death-rate
in the Empire, with the exception of West Africa, where the mean annual
mortality of whites at Sierra Leone was 362 per 1,000!
Conditions in the West Indies began to improve definitely from about
1850 onwards. At that time there was no effective knowledge of the
organic cause of Yellow Fever, nor, for that matter, of any other
tropical disease. Only lately has the basic reason for this early
improvement become obvious. From about 1850 onwards the water-supply
in the more settled parts of the West Indies, and notably in the
larger towns, came to be arranged by pipes. Now these towns were the
special resorts of the Yellow Fever mosquito. The removal of open
standing water, the enclosure of water-supplies, and the introduction
of ordinary modern sanitation in the clearing away of rubbish, did good
work without any knowledge of the organic cause of the disease.
We now know the life-course of the Yellow Fever mosquito. We know
her breeding habits and how the water-living larvae congregate
specially in the small collections of water in the neighborhood of
houses. Precautions have been taken against them and under favorable
circumstances the disease has completely disappeared in well-managed
districts under British and American control. The romantic story of
the destruction of Yellow Fever in the Panama zone, in Cuba, Puerto
Rico, Jamaica, Barbadoes, Trinidad, New Orleans, has been too often
recited to be detailed again. Every one has heard of the tragic event
in connection with the American Mosquito Commission of 1900 and of the
death of Lazear. He and his colleagues, led by Walter Reed (1851-1902),
finally proved that the disease is never conveyed by bedding, or by
clothes, or by other objects, but always and only, in nature, by the
bite of an infected mosquito.
During the experiments of the American Commission, cases of Yellow
Fever were produced in volunteers by bites of infected mosquitoes, by
injection of blood of infected patients, and by injection of _filtered_
blood serum of infected patients (p. 74). With this knowledge in his
hands, the American chief sanitary officer of Havana, William C. Gorgas
(1854-1920), began to destroy mosquitoes systematically and to treat
all Yellow Fever patients under mosquito nets. Within three months
Havana was free from Yellow Fever for the first time for one hundred
and fifty years. These wonderful results are brought out by a table:
_Deaths in Havana from Yellow Fever._
_Year._ _Deaths._ _Year._ _Deaths._
1885 165 1895 553
1886 161 1896 1,282
1887 532 1897 858
1888 468 1898 136
1889 303 1899 103
1890 308 1900 310
1891 356 1901 18
1892 357 1902 0
1893 496 1903 0
1894 382 1904 0
Except for the semi-civilized states of Central and South America,
Yellow Fever is now generally under control. It is perhaps not always
realized, however, that, while the local extinction of this disease
may be among the future triumphs of modern science, its substantial
control over large areas is part of the history of world hygiene (p.
278), and that it is part of the very same movement that has made our
own cities healthier and more habitable than they were in the Middle
Ages.
(b) _Malaria._
The history of Malaria, which is also carried by a mosquito, is very
different from that of Yellow Fever. Malaria was, till recent times,
a disease of temperate as well as of tropical countries. The old name
for the disease is _Ague_. The word _Malaria_ is of no great antiquity
in the English language. It came into use only in the eighteenth
century. Like the word _Influenza_, it is of Italian origin, and,
like _Influenza_, it carries with it a forgotten pathological theory.
_Malaria_ is simply _mal aria_, that is, ‘bad air’. So _Influenza_
is _the influence_, that is to say, the influence of unpropitious
planets or comets that were held to rain down poison into the air. It
was believed that these diseases were the result of local atmospheric
conditions. In Rome and the Campagna the natives still believe that
just as the sun goes down the air becomes specially poisonous.
While the _term_ Malaria is comparatively modern, nevertheless,
recognizable accounts of the _condition_ are perhaps more ancient
than those of any other disease. Of all diseases produced by
micro-organisms, Malaria has perhaps changed its type least during the
course of historic time. The disease is distinctly described in several
places in the _Hippocratic Collection_.
The conception of diseases as separate entities is, of course, modern.
In the case of most infectious diseases, therefore, we cannot hope
to follow the history very far back. But the symptoms associated
with a malarial attack are so definite that there is no difficulty
in tracing the disease with certainty as far back as 1000 B.C. The
real division into ancient and modern times comes, for this disease,
with the use of Cinchona, which is the plant from which Quinine (p.
326) is now derived. Very soon after the introduction of Cinchona in
the seventeenth century, fevers came to be habitually divided into
those which respond to Cinchona and those which do not. Cinchona--and
therefore its derivative, Quinine--is one of the drugs that we owe
to the discovery of the New World (p. 95). The rind of the Cinchona
tree was taken as a remedy by the aborigines. In Europe, where it was
introduced by Jesuit missionaries, it became known as ‘Jesuits’ bark’.
It was popularized by Sydenham (p. 100) and has ever since been widely
used in medicine.
[Illustration: FIG. 122. GEOGRAPHICAL DISTRIBUTION OF INDIGENOUS
MALARIA IN ENGLAND AND WALES ABOUT 1860.]
Sydenham gave a good description of Malaria. During the seventeenth
and eighteenth centuries epidemic after epidemic of ‘Ague’ swept over
England as over other European countries. These epidemics spread from
their endemic centers, the low-lying ill-drained, swampy districts,
where the Malaria mosquito could breed freely in the slowly flowing
water. Of such places the principal in England were the Fens of
Cambridgeshire, Lincolnshire, and the surrounding counties, the marshes
on either side of the estuary of the Thames in Kent and Essex, the
marshes of Romney and Pevensey on the South coast, and those around
Bridgewater near the Bristol Channel (Fig. 122). There Malaria was
never absent, though it differed greatly in prevalence and severity in
different years. Ague remained prevalent in London as late as 1859.
The proportion of ague cases to the total number of in-patients and
out-patients at St. Thomas’s Hospital in London from 1850-60 varied
from between 12 per 1,000 at lowest to over 60 per 1,000 at highest.
Thus, over one-twentieth of the patients in a large London hospital
suffered from what we now regard as a tropical disease, within the
lifetime of men who are still with us!
In London the rise in the value of land led to the erection of the
Thames Embankment, which effectually reclaimed the land around
the river. Extensive works of drainage were at the same time being
undertaken in other infested districts. These soon had their now
well-known effect. In 1864 Malaria was found to be rapidly diminishing
everywhere, and to have left many of its old haunts. The disease
retreated rapidly. At the beginning of the twentieth century a
systematic search was made for a native case in England. After much
labor one single case was at last found. It may safely be prophesied
that native Malaria will never again be anything but a rare disease in
any temperate country with an efficient sanitary service.
The story of the discovery of the malarial parasite is worth
recounting. These organisms inhabit the red blood corpuscles and
were first seen by Alphonse Laveran (1845-) in 1880 in Algiers. His
observations were extended by French and Italian observers, who showed
that the sudden rise in temperature in Malaria coincides with a process
of division of the parasite. Later the suggestion that the parasite
might be conveyed to man by the mosquito was made by Patrick Manson
(1844-1922). The matter was clinched in 1898 by Ronald Ross (1857-),
who showed that the malarial parasite necessarily passes through a
stage in the stomach of the mosquito. The process was first traced by
Ross in a malarial parasite that is peculiar to certain birds, and
was subsequently demonstrated for the allied species of parasite that
produces human Malaria.
We have here an illustration of the value of comparative pathological
studies. Since the demonstration of the life-cycles of the malarial
parasites of man (Fig. 123), the chief attention of hygienists
interested in
Malaria has been directed to the mosquito (Fig. 124). Controlling the
breeding of the mosquito has proved the best method of reducing the
incidence of the disease. Engineering and sanitary works in some places
previously infested with Malaria have had the effect of almost entirely
eliminating disease. The classical instance is the Panama zone, where,
as is well known, the two mosquito-born diseases, Yellow Fever and
Malaria, have disappeared. There are now many areas in the Tropics,
previously infested, in which the disease is almost unknown. There are
many devices for dealing with the mosquito larvae.
By advances such as have been made in the knowledge of Yellow Fever and
Malaria, those areas of the Tropics which are under proper sanitary
control have become far safer habitats. There is good hope of an early
and rapid extension of the process, ultimately rendering new areas of
the Tropics suitable for permanent habitation by the white races and
healthier and happier places for the colored.
[Illustration: FIG. 123. THE LIFE-HISTORY OF THE PARASITE OF MALARIA
The life-histories of the parasites of the malarial diseases of man
have been completely traced. The parasites run through a double cycle,
one in man and the other in the mosquito. In our diagram the cycles of
only one species are represented; there are however two other special
malarial parasites in man.
On either side the head of the mosquito involved is diagrammatically
shown, just below the ‘cycle in man’.
In man the parasites conveyed by the bite of the mosquito (32) or
formed by a division of a parasite already in the blood (7) make their
way into the red blood corpuscles (1 and 2), develop there (3 and
4). Some of them ultimately divide to go through the same cycle (5,
6, 7 and back to 1, 2). The process of division corresponds to the
period of fever. Others develop into crescent-shaped bodies (8, 9 and
10), which can be differentiated into two slightly different forms
corresponding to two sexes (9 male, 10 female). These, if sucked up by
a biting mosquito of the right species, pass into the animal’s stomach
where they develop further (11, 12, 13 male; 14, 15, 16 female) and
end by dividing into forms which conjugate (17). The resultant of this
conjugation or union of the two sexes (17) develops into a lanceolate
form (18, 19, 20) which passes into the cells of the mosquito’s stomach
(21, 22) and finally penetrates these cells (23). The parasite then
secretes a cell-wall and forms a ‘cyst’ (24), which enlarges (25).
The enlargement continues while the nucleus breaks up (26, 27, 28).
In the cyst, which is still growing, a large number of needle-like
forms develop, each of which contains a fragment of the nucleus (29).
Finally the cyst bursts (30), the needle-like forms are cast forth into
the body of the mosquito, and ultimately lodge in her salivary glands
(31). When the mosquito bites another man, she injects some of her
saliva into him through her proboscis. Thus she infects his blood with
some of the needle-shaped parasites that lurk in her salivary gland
(32). So the cycle is re-enacted again and again. We may note that to
prevent this process of repeated reinfection it is only necessary to
break either cycle at one point. Thus destruction of mosquitoes or of
their breeding-places will suffice, or, again, protection of human
hosts from bites of mosquitoes will be sufficient. Either process, if
persisted in, will lead to the extinction of the parasite in the region
under supervision. In England both methods have been in operation and
the disease is almost extinct there so long as any of the malarial
mosquitoes remain in one district. However, the disease can always be
reintroduced by the introduction of subjects of malaria from without.
(From C. M. Wenyon’s _Protozoology_, Vol. II, by kind permission of
Messrs. Baillière, Tindall and Cox. Slightly reduced in size.)]
[Illustration: FIGS. 124 and 125. A common Malaria-carrying mosquito
and a common gnat sometimes confused with the Malaria-carrying
mosquitoes. They are both in sitting posture and may be easily
distinguished by the attitude that they then assume.]
[Illustration:
FIG. 126. CHART OF CASES OF MALARIA reported in Italy in recent years,
showing the seasonal variation of the disease. The date of the year
is written, in each case, below a vertical line corresponding to
midsummer. It will be seen that the maximum incidence is always in
the months July to September, and the minimum incidence is always in
the months January to March. This incidence corresponds to the known
facts of the life-history of the mosquito and of the evolution of the
malarial parasite within the body of the mosquito. ]
§ 15. _The Changed View of Insanity._
Insanity is as old as History. The Bible, Homer, and the _Hippocratic
Collection_, for instance, recount numerous examples of the disease.
Until the nineteenth century there was practically no scientific
knowledge of the conditions classed as insanity. Nevertheless,
hospitals for the insane were instituted at an early date. A well-known
instance is Bethlem Hospital or _Bedlam_ in London, which was developed
as an insane asylum in the fourteenth century.
The new era in the treatment of insanity begins with the abolition of
the old system of restraint. This was primarily due to two noble-minded
men, one a Frenchman and the other an Englishman. Philippe Pinel
(1745-1826), physician at the Bicêtre and afterwards at the Salpêtrière
at Paris, at great personal risk both to his life and liberty,
insisted on freeing from their chains the unfortunate lunatics under
his charge. His _Medico-philosophical Treatise on Mental Alienation_
(1791) was devoted to championing the humaner treatment of the insane.
His contemporary, the Quaker philanthropist William Tuke (1732-1822),
succeeded in 1792 in establishing at York a small retreat for the
insane, where the antiquated, unnecessary and cruel restraints were
abolished (Fig. 127).
While Pinel was beginning the humaner treatment of insanity in France,
considerable interest was aroused in the subject in Germany. There,
however, the medical profession was still under the influence of the
mystical Stahl (pp. 132-3), who regarded all forms of insanity as
perversions of the moral tendencies of the soul, produced by sin!