The Fatal Dance of Washington's Ground Squirrels

This is brought about by the fact that the mice devour the dead bodies of their fellows.

The marked success of the mouse bacillus has stimulated research in this direction, and in the past three years the Pasteur company has had upon the market a germ disease, sold under the name of 'Pasteur virus,' which is said to have yielded gratifying results in the cases of several different rodents.

One favorable condition in the problem so far as the ground squirrels are concerned lies in their cannibalistic habits. So strongly marked is this characteristic that in confinement the squirrels will nearly always leave vegetable food to feed on the carcasses of their companions, which they completely devour. This habit is rather more fixed in the Columbia ground squirrel than in the others, but all of them have it. The same thing holds true in the field under natural conditions, as abundance of evidence proves. From a bacteriological standpoint this habit is of high importance, as it provides a means for the spread of the disease. Special experiments clearly showed that a dead body in a burrow was almost certain to be devoured, and as the diseased squirrel would naturally die in the burrow, an almost perfect means for the spread of a disease exists.

The first experiments inaugurated by the agricultural college were carried out by Dr. A. B. Kibbe and the results have already been published. Dr. Kibbe experimented mainly with known disease germs, such as chicken cholera and swine plague, and demonstrated clearly that the squirrels were susceptible to several bacterial diseases. While the researches are of great value, the results are not such as to admit of being employed in the field, owing to the dangerous nature of the germs used to domestic animals.

The further researches have been carried out at the college by Prof. C. V. Piper and Dr. S. B. Nelson, and the very gratifying results obtained by these gentlemen will soon be published in a college bulletin.

The first work of these gentlemen was to experiment with known disease germs, of which only two that could safely be used offered any promise. The two were the Pasteur virus and the mouse bacillus. The first gave fair results with both the Columbia and Townsend squirrels in the laboratory, but extensive tests made in the field showed clearly that the germ was not a success so far as these animals are concerned.

With the mouse bacillus far more satisfactory results were secured, and it was found that by injecting or feeding a small quantity of a culture of the germ, death would always ensue, usually in 24 hours. Not only this, but the disease would be given to those that fed on the carcass of the diseased victim. In one experiment this was continued through a period of two weeks. With such satisfactory results, much was hoped from this germ, but the field experiments were disappointing, and while some diminution of their numbers was noticed, the disease soon disappeared. These experiments with the mouse bacillus were carried out mainly with the Columbia squirrel, and it is possible that the microbe would prove more efficacious against the other species, an experiment that is in progress.

Incidentally it was found that the mouse bacillus is a very effective agent to exterminate the common native mouse that does so much damage to grain in warehouses, and the disease has been successfully used for this purpose.

From the beginning, however, the hope of the experimenters was to find a native disease among the squirrels and their hopes have been realized so far as the Townsend and Kennicott squirrels are concerned. These two rodents are very similar in size and coloration, but the Townsend squirrel is beautifully spotted, a characteristic lacking in the other.

In 1895 a disease appeared among the Townsend squirrels in limited regions, and during 1896 spread over nearly the whole area inhabited by this animal, causing the destruction of probably 90 percent of the individuals. The introduction of this disease was quite generally attributed to the efforts of Prof. Piper and Dr. Nelson, and it was also claimed that it had spread from a place where the Pasteur virus had been put out. As a matter of fact neither of these statements are correct, and the origin of the disease is not known. Its nature and causes have, however, been assiduously studied for the past three years by Prof. Piper and Dr. Nelson, and it is the results of these studies that make them feel confident they have solved the squirrel problem so far as the two small species are concerned.

The most marked characteristic of the disease as it appeared in 1895 and 1896 was the formation of a large ulcer which nearly always appeared on the neck, but in rare cases was found on the groin or even on the hind leg. After the appearance of this ulcer death ensued in nearly every case. Before death the squirrels usually came out of their burrow and for several minutes indulged in a sort of dance, gyrating rapidly around as if on a pivot until they fell over and with a gasp expired. While undergoing this death dance they seemed completely fearless and one could approach within a few feet and watch the performance. In some sections the disease has been called the 'jim jams,' owing to these strange phenomena preceding death.

The study of this disease was attended with peculiar difficulties. In 1895 no diseased squirrels were obtained until just before they had holed up for the season. Cultures were made from the spleen, liver, kidneys, muscles, heart blood and ulcer pus of the diseased squirrels, and some 20 different bacteria were isolated. Of these two proved to be disease producing, and extensive experiments were carried out with them on guinea pigs and Columbia squirrels, as no healthy Townsend squirrels could be obtained. One of these bacteria, strangely enough, proved to be Mereschkowsky's bacillus, a germ isolated in Russia several years ago by the bacteriologist whose name it bears, and found by him in connection with a native disease of a Russian ground squirrel. The other bacillus is apparently undescribed and is called tentatively by its discoverers 'Bacillus 60.'

The immense series of tests carried out with these two bacilli proved that both of them were very fatal to Columbia squirrels and guinea pigs, and in the case of the former animal the disease spread owing to their cannibal habits. In 1897, when healthy Townsend squirrels were again obtainable, they likewise were found susceptible. Tests made on chickens, dogs, cattle and hogs demonstrated that these animals were not affected by the germs, and therefore large quantities of the germs were distributed this season to determine their value in actual tests. The results as a whole are fairly satisfactory, especially with the Mereschkowsky bacillus. One disappointing feature of the work was that in none of the inoculated Townsend squirrels did the characteristic ulcer appear. Mereschkowsky's disease does not produce this, nor was it obtainable with Bacillus 60. In the researches of this year a squirrel with a nearly healed ulcer was found within a batch of healthy ones, and a series of cultures made from it, and the professors' hearts were gladdened when they found later that they had the bacillus which causes the ulcer-forming disease. This has been demonstrated by many trials in the laboratory, the characteristic ulcer appearing in nearly every case and the bacillus that causes it being found in the pus as well as in the spleen. The germ appears to be entirely new to science and for the time being is simply called 'Bacillus 217.'

No tests have yet been made with it on the domestic animals, but as the disease was all over the region infested by the Townsend squirrel in 1895 and 1896, without affecting any other animals, it is practically certain that it is harmless to them. However, complete tests will be made to determine this, as the investigators are determined to take absolutely no chances in introducing disease germs that might affect farm animals.

It is planned to distribute all three of these germs in large quantities early next season, and the crucial test of the value of the disease will be made. Prof. Piper and Dr. Nelson are both confident that their Bacillus 217 will be the effective means of keeping the Townsend and probably the Kennicott squirrels in check. Since the disappearance of the disease a year ago the former species has multiplied very rapidly and by next year will be fully as abundant as ever. The patience and enthusiasm of the professors has been constant and it is to be hoped that their remarkable results obtained in their laboratory will be duplicated in the field.