make up the precautions ordinarily taken to prevent the rats from
getting on ships. As stated above, they are based on the assumption
that these are the common avenues of entrance. That these precautions
do much good can not be doubted, but in the writer’s opinion they do
not entirely cover the case, for there remains one other road of
ingress, one of the important, if not the most important, which these
precautions do not and can not block and through which rats constantly
get on board, and that is through the medium of the cargo itself.
There is at present nothing to prevent access in this manner to a
vessel and the route is so easy that there can be no doubt that whole
families of rats are carried on board in this way. In fact some
articles of cargo offer inviting harbors and homes to rats,
particularly when these articles have been stored for a time in
rat-infested warehouses. Among such articles of cargo may be mentioned
crockery or china packed in hay or straw or excelsior and loosely
crated; various articles of furniture packed in excelsior, wrapped in
gunny, and loosely crated; wheat, corn, oats, peanuts, or barley when
shipped in bags; and matting in hollow rolls when sewed up in gunny.
Any of these articles could easily become the home of even an entire
rat family after having been stored for a time prior to shipment in a
rat-infested warehouse. As a matter of fact, the last plague rat
discovered in San Francisco was found in a bag of peanuts on the third
floor of a warehouse.
That rats are thus carried on board is absolutely certain in my
opinion. In the recent antiplague campaign at San Francisco there were
ample opportunities for observations along this line, and in no other
way can the presence of rats in troublesome numbers on board certain
vessels be explained. These vessels were new, were freed from rats by
careful and repeated fumigation, and between these acts touched at no
wharves save in Honolulu and San Francisco, where constant antirat
precautions were observed. And yet on their second trip (about five
months after the fumigation had been discontinued) they were badly
rat-infested. Of course, by no means had all these rats been carried
on board in cargo, but the original patriarchs of the colony had,
after which, as is probably the case in all rat-infested ships, their
natural prolific characteristics did the rest.
In the same way, too, rats are carried from ship to shore and the
truth of Kitasatso’s aphorism that “wherever ships go, plague will
go,” at once becomes apparent, and any regulations to prevent the
introduction of such vermin and the plague which they may carry to be
effective must include the inspection of cargo to insure its freedom
from rats, this inspection to be made just before it goes on board.
The relation these rodents bear to plague and the part they play in
its transmission have been thoroughly discussed and set forth in
another article in this work. The work of Ashburton Thompson in
Australia and of the British Medical Commission in India was a
scientific demonstration that plague was primarily a rat disease
transmitted by fleas, while McCoy in the United States has gone
further probably than anyone else in demonstrating the manner in which
the flea does this work. The importance of this relation is emphasized
and the difficulty of ridding a port of pest infection is explained by
a fact, first observed so far as I know by Klein, of London, that rats
suffer from a chronic form of pest, not fatal, at least for a long
time, and during the course of which the rat may exhibit practically
his normal activity. This fact then, that plague is primarily a rat
disease and that it may occur in the rat in a chronic form, shows how
great the danger may be from their presence on shipboard, explains why
it is that where ships go plague will go, and emphasizes the
importance of destroying them on shipboard apart from the damage and
loss which their presence entails.
So important is this and so preeminent is the rôle played by the rat
in plague transmission and propagation that I believe regulations
should demand that all ships be disinfected at least three times, and
better still, four times, a year, for the destruction of rats. If this
precaution were taken, and if to it were added an inspection of cargo
at the port of embarkation to insure its freedom from rats, I believe
the disinfection of cargo could be entirely dispensed with. It is
infectious only in so far as it harbors rats, and if these are not
present disinfection, in my opinion, does as little good in preventing
plague as dipping ballast did in preventing yellow fever.
FUMIGATION.
Once the rat has gained access to a vessel, what is the best method of
getting rid of him?
There are several methods, all of which are effective if properly
used, and all of which depend on sulphur dioxide as the destructive
agent. The following are mentioned: Pot and pan, sulphur furnace,
Clayton system, and Marot system. A choice of one of these methods
will be determined by the cost, the rapidity of fumigation desired,
and the condition of the vessel, whether empty or loaded. No matter
which method is selected, to be effective the sulphur dioxide must be
simultaneously delivered to or generated in every compartment on the
vessel.
For an empty vessel nothing is so satisfactory as the pot and pan
method of generating the gas. It has the following advantages; is more
rapid than any other, is cheaper, is more effective, and is equally
applicable to the largest and the smallest vessel afloat. With a
sufficient number of pots and pans 3,500 pounds of sulphur can be
burned just as quickly as 100. Ten pounds of sulphur in each of 350
pots will be consumed just as quickly as will 10 pounds in any one of
that number, namely, in less than five hours, a fact which was
demonstrated over and over in the outgoing work in San Francisco.
At the beginning of this work it was thought a 2½ per cent gas with
three hours’ exposure would be sufficient. Practice proved, however,
that this was not effective and the strength of gas was increased to 3
per cent and the exposure to five hours which a test, extending over
twelve months and embracing over 3,000 vessels, proved to be ample.
The best pot in which to burn sulphur is 6 inches deep, has a flare of
6 inches—that is, the diameter at the top exceeds the diameter at the
bottom by that much, is from 16 inches to 24 inches in diameter at the
top and has four hemispherical legs about the size of half a billiard
ball. These pots when in use are set in a galvanized iron tub. These
tubs contain a little water, and are of a diameter 6 inches greater
than the top of the pot. The hemispherical legs of these pots will not
punch holes into the tub. The pots are filled with sulphur, which is
hollowed out into a little crater at the top, into which crater from 4
to 6 ounces of alcohol are poured and when all are ready a lighted
match is dropped into each little crater and the compartment is
closed.
In actual practice it was found that an exposure of five hours to a 3
per cent gas would not destroy all the rats in absolutely every case.
Some ships afford better hiding places than others, and on these an
occasional rat would escape. It was the custom, however, to fumigate
all vessels every thirty days and after the third fumigation, on
vessels that did not carry general cargo, no more rats were obtained,
though the fumigations were continued for a number of months.
On those vessels that carried miscellaneous general cargoes a few rats
were found after almost every fumigation. These vessels touched no
wharf from the time they left San Francisco until their return, except
for a short time in Honolulu, where adequate precautions were
observed, and it is difficult to understand how these rats got on
board if they were not carried on in cargo.
For vessels with cargo in their holds the pot and pan method is
dangerous owing to the possibility of fire. For these vessels one of
the other methods of generating the sulphur gas must be used. This
involves the use of an expensive plant consisting of a furnace,
cooling chamber, blower, or fan, and a system of mains and delivery
pipes by means of which the gas is delivered to the various holds and
compartments of the vessel. To be at all effective the gas must be 4½
per cent strength, with at least twenty-four hours exposure. The one
recommendation of such a system is its freedom from danger by fire. It
is too slow; the pipes, even where 6 inches in diameter, are liable to
clogging with sublimed sulphur, an inevitable result if the fans are
driven too rapidly, and it is not possible to do more than one or at
most two ships at a time. The inadequacy of such a method when
compared to the work done in San Francisco where we averaged over nine
vessels every day for almost fourteen months is at once apparent. Many
ships now carry their own disinfecting plants, by means of which not
only is sulphur dioxide generated and pumped into a compartment, but
at the same time also the air of this space is sucked out. This
principle is excellent, but in its application the machines used are
wholly inadequate, having a very limited sulphur capacity per hour and
equipped with delivery pipes in many instances only 2 or 3 inches in
diameter. It would be a matter of days to disinfect some of these
ships with the machines they carry. In San Francisco we again and
again used pots and pans to fumigate these vessels, including the very
compartments in which their own machines sat doing nothing.
The Marot system of generating the gas from compressed liquid sulphur
dioxide has in this country been found too expensive to apply to
vessels. Probably no system will effectually destroy all the rats on a
cargo-laden vessel.
SUMMARY.
To summarize then:
1. The rat is found on all vessels, sometimes in enormous numbers, and
is able to adapt himself to all sorts of conditions. He either gets on
board himself or is carried on in cargo. Owing to his seagoing
tendency, his distribution is world-wide.
2. On shipboard, to live he must do damage to either cargo or stores,
or both.
3. Plague is primarily a rat disease; it may exist in the rat in a
chronic form. Hence where ships go plague will go sooner or later.
4. To prevent the ingress of rats and the consequent spread of plague,
ships should observe antirat precautions, and cargo inspection should
be included in these.
5. At stated intervals, three or, better still, four times a year, all
vessels should be fumigated for the destruction of rats.
6. On empty vessels this can best be done by generating sulphur by the
pot and pan method.
7. On laden vessels some special apparatus must be used to generate
the gas. A longer exposure is required, at least twenty-four hours,
and the gas should be 4½ per cent strength instead of 3 percent. It is
extremely difficult by any method to kill all the rats on a
cargo-laden vessel.
THE RAT AS AN ECONOMIC FACTOR.
By DAVID E. LANTZ,
_Assistant Biologist, United States Department of Agriculture_.
INTRODUCTION.
The world has rightly learned to dread rats as disseminators of
disease, and recent efforts to rid cities of the pests have resulted
chiefly from sanitary considerations. Yet the material losses due to
depredations of rats are now, and always have been, a sufficient
argument for their destruction. The requirements of sanitation and
public health are slowly bringing to pass what economic interests
failed to accomplish, namely, a general recognition of the fact that
the rat is a standing menace to prosperity. To point out some of the
many ways in which rats inflict injury and the extent to which they
drain the resources of the people is the object of the present
chapter.
UTILITY OF THE RAT.
Do rats serve any useful purpose? With very slight reservation, the
question may be answered in the negative. There have been times and
places in which the rat’s work as a scavenger accomplished good, but
modern methods of garbage disposal are superseding the feeding it to
rats.
It was Robert Southey, the poet, who, nearly a century ago, humorously
suggested as the first three steps to eradicate rats—first,
introducing them as a table delicacy; second, utilizing the skins; and
third, inoculating them with a contagious disease.[BY] The last of
these plans is now receiving considerable attention from
bacteriologists, but the others, for obvious reasons, have been
neglected.
Footnote BY:
Omniana, vol. 1, p. 25, 1812.
It is true that under exceptional circumstances the rat has been a
source of human food. The principal instances on record were during
the siege of Paris in 1870, and during the siege of the French
garrison at Malta, 1798–1800, when food was so scarce that rat
carcasses brought high prices. Another was on board the ship _Advance_
during an arctic winter, when Doctor Kane attributed his entire
immunity from scurvy to his diet of fresh rats, of which none of the
other members of the party would partake.[BZ]
Footnote BZ:
Second Grinnell Expedition, vol. 1, p. 393, 1856.
The statement is often made in newspapers, and even in encyclopedias,
that in Europe, and especially in France, rat skins are extensively
used in the manufacture of gloves. The late Frank T. Buckland, about a
half century ago, made diligent inquiry in London, and through friends
in Paris and other places on the Continent, but found no confirmation
of such statement. He concluded that either rat skins were not used
for making gloves or the manufacturers were unwilling to acknowledge
such a use.[CA] Personally, the writer has been unable to learn of any
demand or market for rat skins at the present time. They are not
strong, and the fur is of inferior quality. The occasional finding of
one or more rat skins in the fur lining of coats is probably to be
explained by the fact that they are sometimes included in lots of
small muskrat skins (“kitts”) and overlooked by the buyer.
Footnote CA:
Curiosities of Natural History, first series, p. 83, 1857 (Reprint
1900).
DESTRUCTIVENESS OF THE RAT.
Rats inflict injury in a surprising number of ways, and before an
attempt is made to consider the magnitude of the losses due to these
animals a statement of the nature of their depredations should be
made.
DAMAGE TO GRAINS.
Cultivated grains are the favorite food of rats. The animals begin
their depredations by digging up the newly-sown seed. They eat the
tender sprouts when they first appear, and continue destroying the
plants until the crop matures. They then attack the grain itself, and
after harvest take toll from shock, stack, mow, crib, granary,
elevator, mill, and warehouse. When rats are abundant their
depredations amount to an appreciable percentage of the entire yield
of grain, and in exceptional cases whole crops have been ruined.
INDIAN CORN.
Probably this crop suffers greater injury from rats than any other in
the United States. To some extent the animals dig up newly planted
corn, but their injury to the maturing grain is far greater. They are
especially fond of corn in the milk stage, and often climb the upright
stalks and strip the cobs bare. In this way sometimes whole fields are
destroyed.
Corn in the shock is often attacked by rats, especially in parts of
fields adjacent to hedges, drains, or embankments that afford shelter
for the animals. A pair of rats often make a corn shock their home,
and soon destroy both grain and fodder.
Corn in cribs is often damaged by rats. Many cribs are built close to
the ground, and rats take up their abode under the floor. They soon
gnaw through the wooden barrier and have free access to the grain.
They shell the corn and eat the soft part of the kernels, wasting much
more than they eat. They carry the grain into underground burrows and
bring up moist soil from below, which in contact with the grain makes
it moldy and unfit for market or for feeding to stock. A number of
farmers have reported the loss by rat depredations of from a fifth to
a half of the contents of a large corn crib during a single winter.
An Iowa farmer, writing to an agricultural journal, relates the
following experience:
We had about 2,000 bushels of corn in three cribs to which rats ran,
and they ate and destroyed about one-fourth of the corn. Much of it
was too dirty to put through the grinder until it had been cleaned
an ear at a time. All the time we were poisoning and trapping the
rats. We killed as high as 300 rats in two days and could hardly
miss them. They destroyed more than enough corn to pay taxes on 400
acres of land.[CB]
Footnote CB:
Missouri Valley Farmer, April, 1907.
Throughout the United States, but especially in the West and South,
corn is often stored for months in rail or other open pens, to which
rats have free access. Often the loss in a single season would pay for
the construction of rat-proof cribs, or at least for wire netting,
that would fully protect the crop.
SMALL GRAINS.
Much has been written about the rat as a house and barn pest, but its
depredations in the fields have usually been overlooked. In some
localities the common rat, as well as the house mouse, swarms in the
fields, especially in summer, and subsists entirely upon the farmers’
crops.
Stacked grain is peculiarly exposed to rat depredations. In the United
States, although the cost of protection is small, rats are seldom
fenced away from stacks, and, if threshing is delayed, serious loss
results. Often, at the removal of a stack, large numbers of rats are
discovered, which have been living at the expense of the farmer. As
early as 1832 a farmer in Frederick County, Md., with the help of men
and dogs, killed 217 large brown rats from one stack of rye.[CC] In
England instances are on record of the killing of over a thousand rats
from one stack of wheat.
Footnote CC:
Am. Turf. Register, vol. 3, p. 632, August, 1832.
The destruction of feed by rats is a serious loss not only on the farm
but also in city and village. The feed bin or barrel is often left
uncovered and rats swarm to the banquet thus exposed. Small feeders
suffer greater proportional losses, for managers of larger barns
recognize the enormous drain and usually provide rat-proof bins, if
not rat-proof stables. When rats have access to a stable they take a
good share of the feed directly from the mangers, but the loss is
seldom noticed.
Rats are exceedingly fond of malt, and in malt houses and breweries
constant watchfulness is needed to prevent losses. Mills, elevators,
and warehouses in which grain and feed stuffs are stored are subject
to constant invasion by rats and mice.
A full-grown rat consumes about 2 ounces of grain daily. A half-grown
rat eats nearly as much as an adult. Fed on grain, therefore, a rat
eats from 45 to 50 pounds a year. The cost depends somewhat on the
kind of grain. If wheat, the value is 60 to 75 cents; if oatmeal,
about $1.80 to $2. Several feeders of horses in Washington, D. C.,
estimated the cost of keeping each rat on their premises at $1 a year.
Even though half the grain eaten is waste, the direct loss from this
source to feeders is enormous.
MERCHANDISE IN STORES AND WAREHOUSES.
The loss from depredations of rats on miscellaneous merchandise in
stores, markets, and warehouses, is second only to the losses on
grains. Not only are food materials of every kind subject to attack,
but the destruction of dry goods, clothing, books, leather goods, and
so on is equally serious. Merchandise other than foodstuffs is usually
destroyed for making nests, but books and pamphlets, especially the
newly bound, and some other articles, furnish food in the glue, paste,
oils, or paraffin used in their manufacture. Some kinds of leather
have a peculiar attraction for rats, while others are never touched.
Shoes are seldom gnawed unless they have cloth uppers or are made of
kid. New harnesses are not often attacked, except collars, which
contain straw, and cruppers, which are stuffed with flaxseed. Old
harness leather is salty from the perspiration of horses, and rats and
mice gnaw it for this reason. Kid gloves and other articles made of
similar leather are often destroyed by rats.
Lace curtains, silk handkerchiefs, linens, carpets, mattings, and
other dry goods in stores are often attacked by rats. Some of the
stuffs contain starch, which serves as food, but most of them furnish
nesting materials only. A slight injury makes these articles
unsalable; this is especially true of white goods, which are easily
ruined by soiling. Nearly all large dry goods and department stores
suffer heavy losses from rats. Grocers, druggists, confectioners, and
other merchants also have similar experiences, and to the direct
losses must be added the sums expended in fighting the pests.
MERCHANDISE IN TRANSIT.
Merchandise billed for shipment often lies for days in stations and
warehouses or on wharves, where depredations of rats and mice cause
heavy losses to shippers and consignees. Similar losses occur on boats
carrying merchandise from port to port.
Fruits and vegetables in transit on steamboats are often destroyed or
damaged by rats. Tomatoes, cucumbers, sweet potatoes, bananas,
oranges, grape fruit, peanuts, and similar produce shipped by water
from the South, especially in winter, reach northern markets with a
large percentage of loss.
In view of the practicability of destroying rats on ships by
fumigation, and the ease with which rat-proof compartments for stowing
produce can be constructed, it would seem that losses of this nature
should be entirely prevented.
POULTRY AND EGGS.
Aside from disease, the greatest enemy of poultry is the rat. The loss
from rats varies with their abundance and the care taken to exclude
them from the poultry yard. The magnitude of the damage is not
generally known, because much of it is blamed on other animals,
particularly minks, skunks, and weasels. Much of the injury occurs at
night, and the actual culprit is seldom detected. Farmers have heard
that minks, skunks, and weasels prey upon poultry. What more natural
than to conclude that one of these animals is doing the mischief,
especially if one has been seen about the premises?
Rats often prey upon small chicks, capturing them in the nests at
night or even about the coops in the daytime. The writer has known
rats to take nearly all the chicks on a large poultry ranch, and over
a large section of country to destroy nearly half of a season’s
hatching. Young ducks, turkeys, and pigeons are equally liable to
attack, and when rats are numerous, are safe only in rat-proof yards.
A writer in a western agricultural journal states that in 1904 rats
robbed him of an entire summer’s hatching of three or four hundred
chicks.[CD] A correspondent of another newspaper says, “Rats destroyed
enough grain and poultry on this place in one season to pay our taxes
for three years.”[CE] When it is remembered that the poultry and eggs
marketed each year in the United States have a farm value of over
$600,000,000, it will be seen that a small percentage of loss
represents an enormous sum.
Footnote CD:
Homemaker (Des Moines, Iowa), May 27, 1907.
Footnote CE:
Missouri Valley Farmer, April, 1907.
The destruction of eggs by rats is great, not only on the farms where
they are produced, but also in the markets. Commission men and grocers
complain of depredations upon packed eggs. The animals break and eat a
few eggs at the top of a case and the broken yolks run down and soil
the eggs below. Then, too, rats carry away unbroken eggs, displaying
much ingenuity in getting them over obstacles, as up or down a
stairway.
A commission merchant in Washington, D. C., states that he once stored
100 dozen eggs in a wooden tub in his warehouse and left them for
nearly two weeks. He then found that rats had gnawed a hole through
the tub, just under the cover, and had carried away 71½ dozen, leaving
neither pieces of shell nor stains to show that any had been broken.