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Bats are not

the only

agents in spreading plague, but

at the com- mencement they are often the principal agent.

This fact has not been

sufficiently realised

even now.

Statement of the precautions to be taken

against the

rat.

Destruction of rats and mice in a

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9. It is not affirmed that rats are the only agents in the spread of plague. They are not likely to carry the infection to distant places unless sick or dead rats are transported in merchandise or in bags of grain. Mon as a rule is the chief importer of plague into a locality, while the rat at the commencement is generally the chief disseminator. Over and over again the history of plague records first of all the arrival into a healthy district of a man or woman infected with plague or with infected clothing; later, a mortality among the rats af the house or neighbourhood, and finally an outbreak among the inhabitants. There is one form of plague which may take a different course, and that is pneumonie plague. This disease is very infectious from man to man, and there may be an outbreak with or without the assistance of the rat. Further than this, when an epidemic is once established. the importance of the rat ns a disseminator of the disease decreases in proportion to the number of cases of the disease, and it may happen that a severe epidemic prevails without it being possible to find either a sick or dead rat.

10. The importance of the rat as a disseminator of plague has not, until recently, been grasped any more effectually in Europe than it was in the East. In Oporto, the usual history repeated itself, as it is still likely to be repeated elsewhere in future epidemics. In Oporto, rats and mice were observed to be dying in the docks and their neighbourhood several weeks before the first case of plague occurred among the wharf porters. The sign of danger was obvious in the mortality of rats, but it was not under- stood. In the meantime, plague was not only established at Oporto, but it was carried by Portuguese sailors to Paraguay in South America, where by similar means it has obtained a hold on the American Continent.

11. The precautions to be taken for the prevention of the spread of plifgue so far as rats are concerned consists in (a) the destruction of as many rats as possible in a healthy country before there is any importation of plague, (4) the prevention of sick or dead rats being transported and imported by merchandise or grain into a country, and, (e) in the event of importation of plague, the destruction and extermination with the earliest promptitude of rats, not only in the locality where the rats are dying, but also in the adjacent localities.

12. Measures undertaken with the object of destroying as many rats as possible in a country which has relations, territorial or commercial, with an infected locality reduces an influential source for the propagation of the disease, and if that destruction can be effected before plague is imported, the chances of the disease developing into an extensive epidemic is very much lessened. It is with this view that in Denmark, France, and Algeria the destruction of rats has been begun, a small sum adopted for being given for so many rats that are killed. The means adopted

healthy country before plague is imported, and the

methods

this purpose.

ย

are the employment of the rat catcher, poisoning by the use of arsenic, phosphorus and strychnine mixed with other substances, and the suffocation of rats by the propulsion of sinoke, sulphur fumes, or sulphide of carbon into their runs or into drains, By the latter method a large number of rats have been destroyed in Algeria. The drains and sewers were stopped up, and the rats suffocated by fumes of sulphurous acid and sulphide of carbon pumped in. Crude carbolic acid also is a useful agent to be used when the rats are dying of plague. Poured down the holes and runs it served its purpose in Calcutta. Carbolic acid is also a disinfectant, the smell of which, according to Hankins's experience in India, is particularly disliked by rats, and the use of which will assist in driving them from a house or building.

Mice can be got rid of by infecting a few with Loettler's typhi murium bacillus. It sets up in them a train of symptoms not unlike typhoid fever, and is highly infectious among mice. Smail pieces of bread soaked in the fluid containing the bacilli may be placed in front of the mouse holes, or one or two mice may be caught and inoculated and then allowed to escape. The mice infect one another and the healthy feed on the bodies of those that have died, so that soon a destructive epizootie is raging among them. It was by setting up an epidemic of this kind in Thessaly when the crops were being destroyed by an enormous number of field mice, that the remainder of the harvest was saved.

The disease does not affect other animals besides mice and, unfortunately, the rat is only but slightly affected by it. A similar microbe, other than plague, has still to be found for the rat, and should be the subject of laboratory experiment."

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13. To prevent the importation of sick rats from an infected Measures to port, rats on board ship should be destroyed at the port of depar- be adopted to ture, on the voyage, and at the port of disembarkation. The de- prevent the struction of rats on board ship is peculiarly difficult, and no method of sick rats. hitherto devised can be said to have proved entirely satisfactory.

importation The safest, least offensive, and most convenient during the yoyage is probably the generation of carbonic acid gas in the hold three or four days before arrival in port. It is one which is recommended by M. Pierre Apéry to the Sanitary Council at Constantinople. The carbonic acid gas, by its density, spreads over the lower part of the hold and gradually penetrates into the crevices and holes, Any animal venturing into this lower stratum of the gas rapidly dies. The gas is odourless, nou- inflammable, and not injurious to merchandise. generated by mixing chalk and a dilute acid in a leaden vessel It is easily or in a wooden trib that has been tarred. Nearly 24 lbs, avoir- dupois of chalk give 8 cubic feet of carbonic acid gas. The acid required for this would be nearly 24 ils, of oil of vitriol,

• Since this was written Danys has obtained some excellent results in destroying rats in Paris by inoculating a few with a pathogenie cocco-bacillus which caue in them a fatal infectious disease,

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