Part 20

Pfreimbtner,[BU] 1904, sees the reason for a partial failure in the application of Loeffler’s bacillus to the destruction of field mice. In the use of a solid medium (agar-agar), upon which the bacterial cultures only grow upon the surface, too few bacteria are transferred to the pieces of bread, and consequently too few virulent bacteria are consumed by the mice. An active infection depends not upon the existence of virulent bacteria, but rather upon the entrance of a definite number of virulent bacilli.

Footnote BU:

Pfreimbtner, J.: Erfahrung über des Loeffler’schen Infektionsverfahren zur Bekämpfung der Mäuseplage in einer neuen Art der Anwendung. Fühlung’s landw. Zeit., 1904, p. 619. Rev. by Schander in Centblt. f. Bakt., 2. Abt., vol. 15, 1905, p. 502.

The author used skimmed milk as a nutrient medium and describes a series of 9 experiments and gives an estimate of the cost of the process with the use of milk instead of agar. The advantage of the use of milk is in the greater certainty of the results and cheapness as compared with other methods. The bread cubes impregnated with skimmed milk were well taken by the mice and desiccation of the cultures, which not infrequently occurs in the use of more solid media, is excluded. Notwithstanding the excessive thinning, the liquid still contains many virulent bacilli. The washing out of bacilli after rain is slightly less possible as in the use of the more solid media. The action of light, where the bread cubes contain many bacilli, is insignificant, and hence the carrying out of the process in the daytime is made possible. Milk is easily obtained and the thinning and application less bothersome. Finally the author expresses himself against the view that the _B. typhi murium_ causes serious diseases in man.

Teichert,[BV] 1905, speaks of Loeffler’s mice typhus bacillus and Pfreimbtner’s method of growing it upon sterilized skimmed milk. A number of experiments carried out at the bacteriological laboratory of the Vreschen experiment station shows the utility of Loeffler’s bacillus for the destruction of house and field mice. The long-tailed field mouse was, on the other hand, not harmed by it.

Footnote BV:

Teichert: Die mechanischen, chemischen und bacteriellen Kampfmittel gegen Ratten und Mäuse. 2. Teil: Die Bekämpfung der Mäuse. Fühlung’s landw. Zeit., 1905, No. 16. Rev. by Ehrenberg in Centblt. f. Bakt., 2. Abt., vol. 15, 1905, p. 503.

Bahr,[BW] 1905, gives a complete and satisfactory summary of the literature upon the subject of the destruction of rats and mice with bacteria, including original work of his own.

Footnote BW:

Bahr, L.: Ueber die zur Vertilgung von Ratten und Mäusen benutzten Bakterien. Centblt. f. Bakt., Orig., vol. 39, 1905, p. 263.

Zielander,[BX] 1908, obtained fairly good results with Danysz virus in the laboratory, also with ratin. No fixed tests were recorded.

Footnote BX:

Zielander: Der Rattenbacillus als Rattenvertilgungsmittel. Arb. a. d. k. Gesndhtsmte., Berl., vol. 28, 1908, p. 145.

RÉSUMÉ.

Rats are notoriously resistant to bacterial infection. Even plague usually fails markedly to diminish their prevalence. An epizootic of bacterial nature, therefore, can not be classed with the natural enemies of the rat. We are not surprised, then, to learn that the bacterial viruses have signally failed to accomplish their mission.

These bacterial viruses belong to the colon-typhoid group of organisms. They are either identical with or closely related to the original bacillus of mouse typhoid discovered by Loeffler, or the para-typhoid bacillus type B, which is frequently the cause of meat poisoning, or the _Bacillus enteritidis_ of Gærtner, which has been associated with gastro-intestinal disorders.

The claim that these rat viruses are harmless to man needs revision, in view of the instances of sickness and death reported by various observers. The pathogenicity for man depends upon the virulence of the culture, the amount ingested, the nature of the medium in which it grows, and many other factors.

Danysz virus is pathogenic for rats under laboratory conditions, but has feeble powers of propagating itself from rat to rat. It rapidly loses its virulence, especially when exposed to light and air. The result depends largely upon the amount ingested. The other viruses have proven even less satisfactory.

Under natural conditions these rat viruses may be likened to a chemical poison, with the great disadvantage that they rapidly lose their virulence and are comparatively expensive. They also have the further disadvantage that chemical poisons do not possess of rendering animals immune by the ingestion of amounts that are insufficient to kill or by the ingestion of cultures that have lost their virulence.

PLAGUE ERADICATION IN CITIES BY SECTIONAL EXTERMINATION OF RATS AND GENERAL RAT PROOFING.

By VICTOR G. HEISER,

_Passed assistant surgeon, U. S. Public Health and Marine-Hospital Service, chief quarantine officer and director of health for the Philippine Islands_.

The health officials of the city of Manila, P. I., for the five-year period from 1900 to 1905 made most valiant efforts to destroy the rats of the city; approximately $15,000 were paid in rat bounties and $325,000 in salaries and wages and other expenses for rat catching, but at the end of that time the rats were apparently as plentiful as before and the plague was still present. The experience in Tokio and Osaka had been practically the same. Professor Kitasato expressed the opinion that a given city could only have up to a certain number anyhow, because further increase was limited by the amount of available food, and when the limit had been reached the rats commenced to eat one another, which prevented more than a certain number ever being present, and that the increase by breeding was about as rapid as any method of destruction which had yet been tried.

The following plan was then tried, and the plague among human beings soon disappeared, there being no cases since April, 1906; and it has been eradicated among rats each time that it has made its appearance.

A list of the places at which plague-infected rats were found was made. Each was regarded as a center of infection. Radiating lines, usually five in number, were prolonged from this center, evenly spaced like the spokes of a wheel. Rats were caught along these lines and examined. Plague rats were seldom found more than a few blocks away. The furthermost points at which infected rats were found were then connected with a line, as is roughly shown in the diagram on page 206 (Fig. 59.)

The space inclosed by the dotted line was regarded as the section of infection. The entire rat-catching force, which had heretofore been employed throughout the city, was then concentrated along the border of the infected section; that is, along the dotted line. They then commenced to move toward the center, catching the rats as they closed in. Behind them thorough rat proofing was carried out. One section after another was treated in this way until they had all been wiped out. Once weekly thereafter rats were caught in the previously infected sections and at other places which were insanitary and which had been infected in years gone by. This was continued for one year.

The city was then divided as is shown in the diagram facing this page, and rats are caught once weekly at each point at which the lines intersect and sent to the laboratory for examination.

[Illustration:

FIG. 59.—Isolated plague-infested center, Manila, P. I. ]

In addition, sanitary inspectors are instructed to bring in dead rats which have evidently died of disease, and more detailed rat catchings are made along the water front.

It is understood of course that rat proofing of the entire city should be thoroughly carried out and constantly maintained.

CONCLUSIONS.

1. Since the above system was adopted plague has disappeared in the city of Manila; among human beings in 1906; among rats in 1907, and it has not reappeared since.

2. That the cost is only a small fraction of that of general rat extermination.

3. That the plan is thoroughly practical for any kind of a city.

[Illustration:

FIG. 60.—General Scheme for testing plague rat infection, City of Manila. Sanitary Map Bureau of Health. _Escala 1:38,500_ ]

THE RAT IN RELATION TO SHIPPING.

By WILLIAM C. HOBDY,

_Passed Assistant Surgeon, Public Health and Marine-Hospital Service_.

Since men first went down to the sea in ships the rat’s voyage-making tendencies have been known, and their fecundity is as well established as their fondness for travel. The record does not state that there were more than a pair on the ark at the beginning of her voyage, but the chances are better than even that her skipper began that voyage with more rats than his manifest showed; but whether he did or not, we can be sure he had more at the end of the voyage than at the beginning. Whether or not succeeding generations inherited from their forbears on the ark this well-known wanderlust is undetermined, but it is a fact that the intimacy and companionship established and begun then have been persistently maintained by the rat ever since. His travels have been coextensive with man’s, until to-day there is not a port on earth where the rat is not present. Any exception to this statement simply proves the rule. The rat is cute; he knows when he is well off and his absence from a port does not prove that he has not been there, but that he has been too intelligent to follow man ashore. In establishing this shipboard intimacy there has been no “by your leave” courtesy on his part either; he goes without consent—against orders, even—and man’s ingenuity has as yet discovered no effective means of keeping him off. This is not surprising when the rat’s ability as a rope walker is considered. I have seen a rat gallop with all appearance of enjoyment along an inclined electric cable from a church steeple on one side of a street into the second story of a hotel on the other. Others have been seen traveling along the telephone wires from house to house, and on shipboard they frequently have runways on small pipes along which they scurry in perfect security. When a ship is fended off 6 feet from the dock and her gang plank is lifted or guarded she is still freely accessible, because all her mooring lines are only so many highways along which rats can and do pass with ease and in perfect safety.

This fondness for ships and sea travel is shared by the various species of the rat family, but the _Mus norvegicus_ has earned the reputation of being the greatest traveler of them all. He almost invariably predominated among those killed by fumigation on shipboard. That he finds life on shipboard easy and the conditions satisfactory is proved by the numbers that are destroyed from time to time by fumigation. While in charge of the outgoing quarantine work in San Francisco the chief engineer of a small lumber carrier called to book his vessel for fumigation. The vessel was small, only 260 tons, and carried nothing but lumber and her own ship’s stores, but the chief declared she was overrun with rats, and to prove it showed where they had eaten the patches from his shoes. He declared they robbed him of his sandwich when he came off watch, and requested me to give her a thorough fumigation. This was done. The next morning the agent of the vessel phoned to ask how I measured rats, stating that on this vessel they had collected “a barrelful and seven.” Three hundred and ten on a little vessel of only 260 tons burthen.

On another vessel after one fumigation 100 were collected immediately after fumigation, but a few days later, when the vessel was undergoing extensive repairs, 425 others were found—a total of 525 on one small vessel. These numbers are small, however, when compared with the results obtained on others, i. e., on grain-carrying vessels. For instance, a vessel was fumigated some years since in Bombay where 1,300 were destroyed at one time, and the _Minnehaha_, a new vessel only nine months in commission, on fumigation in London, England, in May, 1901, yielded a bag of 1,700 rats.

ADAPTABILITY OF THE RAT TO HIS SURROUNDINGS.

In addition to his qualities as a sailor and tight-rope walker, the rat has the power of adapting himself to most unusual conditions and surroundings. At the beginning of the outgoing work in San Francisco it was urged that rats either could not or would not live on any part of tank ships engaged exclusively in carrying oil, owing to the fumes and vapors that permeated the entire vessel. This statement was unquestionably correct for those compartments in which the oil itself was stored or carried. It was not true, however, for the superstructure of these vessels, for on one of the oil carriers 60 rats were found after one fumigation, and of the thirty or more vessels of this class that were regularly fumigated in San Francisco, although the odors of oil or gasoline were quite strong in the living compartments, not one was found that did not harbor rats. Still more remarkable, as illustrating the rat’s adaptability, was the fact that from the large refrigerating plants which some vessels carried and in which fumigation had not been practiced for a long time rats were obtained that had grown a fur an inch and a half long to protect themselves from the cold.

DAMAGE TO CARGO.

That rats on shipboard in any such numbers as mentioned above must do much damage to cargo can not be doubted.

Inquiry as to the extent of this damage showed that there were no data on the subject. That such damage was common and considerable, however, was revealed by the fact, elicited by these inquiries, that nearly every steamship company on both the Atlantic and Pacific took precautions both to keep rats from getting on board and to destroy them after they did. One example will show what damage may occur. The British steamer _Gadsby_, on a voyage from India to Antwerp, covering a period of twenty-nine days, had 44,000 out of 46,000 bags of wheat cut by rats, with an estimated damage of $2,200.

The constant and almost universal presence, then, of rats on shipboard can not be doubted, and if it could the results of fumigation, wherever practiced with SO_{2}, would serve to settle the question, for they are found under all conditions, even on the most unlikely vessels.

How do these rodents gain access to a vessel? It has been the custom to assume that they came on board from the docks over the side when this was possible, and when it was not, as when the vessel was fended off or stood too high out of the water, that they made use of the gangways, mooring lines, hawsers, etc., as avenues of communication. It is still the practice, therefore, in enforcing antirat precautions, to compel the ship to fend off 6 feet from the dock, to wear fat funnels on all lines, and to raise the gangway from the dock at night. Just a word as to these precautions. The most practical fender is a floating one made of heavy timbers either bolted together into a solid frame, with the necessary cross braces bolted in, or made up of logs or spars chained together. They should be long enough to distribute the pressure of the vessel as the tide moves over a number of piers or piles so that the weight does not bear, through the medium of these fenders, on just one or two of the wharf foundations. Such a fender will stay in position, will do no damage to the vessel, and no matter how great the amplitude of the tide may be, will always remain below the ship’s gunwale and can not therefore be utilized by rats as a means to get on board. Large vessels require at least two. Small ones need but one, and it was found in San Francisco, in the case of those vessels changing their mooring several times daily, that this one could be carried from wharf to wharf by the vessel without trouble or delay simply by lashing it edgewise outside on top of the guard.

Funnels should be of heavy galvanized iron, circular in shape, and not less than 36 inches in diameter. The spout of the funnel should be 3 inches in diameter and should be at least 18 inches long. The flange of the funnel should be soldered to this 18-inch pipe at its middle so that the spout projects 9 inches out of the funnel and 9 inches into it. When the two halves of the funnel are brought together this spout or tube is occupied by the line or hawser to be protected, and by lashing this tube to the hawser the funnel is held in position and prevented from lying down. Such a funnel should be put on every line from the vessel to the dock, and when the tube does not fit the line the latter should be parceled before the tube is lashed to it.

These, together with raising the gang plank from the dock at night, 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.