Page:Popular Science Monthly Volume 25.djvu/388

376  the subject, and from their labors we shall by-and-by be in possession of the first really accurate and scientific examination of the effects of volcanic eruptions, which in this case bids likely to result, to meteorological science at least, in a gain whose immense importance it is impossible now to calculate. Nor is it unlikely that this "biggest terrestrial experiment" afforded us by Nature may ultimately prove to have been not the least of her beneficent gifts to humanity.—Proceedings of the Royal Geographical Society.



HE important fact that certain viruses may be varied in potency, and that protection against one may be afforded by another less potent, is to-day not only gained for science, but has entered the stage of application. It is obvious that great interest attaches, in pursuing this line of study, to the investigation of methods of attenuation adapted to new virus. I announce to-day an advance thus made in regard to rabies.

In passing from a dog to a monkey, and then from one monkey to another, the potency of rabies-virus decreases at each transfer. After its strength has been thus diminished, if the virus is then transferred to a dog, a rabbit, or a Guinea-pig, it still remains attenuated. In other words, it does not regain all at once the intensity of virus from a mad dog. Only a small number of transfers from monkey to monkey is necessary to bring the virus to such a state of attenuation that it will not induce madness in a dog when introduced hypodermically. Even inoculation by trepanning, that most certain method of communicating rabies, will produce no result except that of causing in the animal a condition of insusceptibility to rabies.

The potency of rabies-virus increases in passing from one rabbit to another, or from one Guinea-pig to another. When it has been brought to a maximum in rabbits, it exhibits its full strength on being transferred to the dog, and is then more potent than virus from a mad dog. Such virus inoculated into the circulatory system of a dog invariably causes madness which results in death.

Although the virus rises in potency at each transfer from rabbit to rabbit, or from Guinea-pig to Guinea-pig, it must pass through several of these animals in order to regain its maximum potency, when this has first been reduced in monkeys. In like manner, the virus of 