The marvel which we witness in the certain and speedy disappearance under the influence of mercury of a large sclerosis as hard as cartilage, is more than equalled by the melting away of a big tumourgumma under that of iodide of potassium." The record of Hutchinson and others may serve to remind us that the successful treatment of syphilis had its beginnings before the advent of recent chemotherapy.

REFERENCES

Bloch, Iwan: Der Ursprung der Syphilis. 2 vols., 1901.

Also a brief history of syphilis in Power and Murphy's System of Syphilis, vol. 1, 1914, pp. 3–39.

Brown, H. M.: Must the History of Syphilis be Rewritten? Bull. Soc. Med. Hist., Chicago, 1917, II, pp. 1-14.

Calkins, Gary N.: "Fritz Schaudinn," Science, N.S., vol. xXIV (1906), pp. 154-55.

Montgomery, T. H., Jr.: "Fritz Schaudinn," Popular Science Monthly, vol. 70 (1906), pp. 274-78.

Sudhoff, Karl: The Origin of Syphilis, and The End of the Fable of the Great Syphilis Epidemic in Europe following the Discovery of the Antilles (translations by A. Allemann), Bull. Soc. Med. Hist., 1917, II, pp. 15–26.

See also obituary notice of Paul Ehrlich in the Proceedings of the Royal Society, series B, vol. 92 (1921), pp. i-vii.

CHAPTER XIX

PREVENTIVE MEDICINE IN THE TROPICS MORE than a century before the appearance of syphilis in Europe the eastern hemisphere was ravaged by another disease which had its origin in the tropics. The Black Death, or Plague, which even since the beginning of the twentieth century has carried off millions of the inhabitants of India, in the fourteenth swept to the northwest and claimed about sixty million victims. This was not its first nor its last visitation of Europe. We have already seen its disastrous effects in London and elsewhere in the time of Sydenham; and within the last twentyfive years this dreaded disease has threatened the ports of Italy, France, Germany, and Great Britain, as well as those of America both on the Atlantic and the Pacific. The virulent outbreak at Hong-Kong in 1894 led to the study of the pestilence in the light of modern bacteriology and parasitology. Within a few months Kitasato and Yersin had discovered the Bacillus pestis. Of the two forms of the disease— the pneumonic and the bubonic- the former may be conveyed from one person to another by means of bacilli borne by the air. Bubonic plague is transmitted to man from the rat by fleas. The chief

preventive measure is the extermination of diseased rats. Haffkine's prophylactic vaccine has a marked effect both in decreasing the chances of infection and in increasing the chances of recovery in cases in which infection takes place.

It was Dr. (afterwards Sir Patrick) Manson who prepared the way for the greatest triumphs of preventive medicine in the tropics by demonstrating thoroughly, in 1879, that the mosquito is the intermediate host of Filaria sanguinis hominis, the parasite in certain particularly hideous forms of filariasis. Manson traced the life-cycle of the nematode in the mosquito and in the definitive host, man. He observed the filaria in the stomach of the mosquito after it had sucked the blood of a patient suffering from filariasis, found that within a few hours they broke down the blood corpuscles in the abdomen of the insect, the escape of the hæmoglobin bringing about a thickening of the plasma. The viscosity of the plasma seemed to stimulate the filaria to wriggle out of their sheaths. Once rid of these they moved about freely and found their way into the thoracic muscles of the mosquito, where they underwent metamorphosis, the young parasites showing a remarkable increase in size. The mosquito, about a week after sucking the blood of the filariasis patient, lays her eggs on the surface of stagnant water, and then dies. The filariæ find their way into the water

from the dead body of the intermediate host, and thence into the stomach of the definitive host, and from the stomach reach the lymphatic trunks. There they attain sexual maturity, and give birth to a new generation of filaria, which eventually pass by way of the lymphatic vessels into the blood stream.

In the year following Manson's discovery of the life-history of Filaria sanguinis hominis, Alphonse Laveran, a French army surgeon on service in Algeria, observed in the blood of patients suffering from malaria parasites which he considered the cause of the disease, a judgment that was soon confirmed by Dr. Richard and others. These protozoa were accurately described by Marchiafava and Celli in 1885. There are three varieties of this group of hæmocytozoa, Plasmodium vivax, Plasmodium malaria, and Plasmodium falciparum, the parasites respectively of tertian, quartan, and æstivo-autumnal fevers. Golgi, the histologist, who as early as 1885 had shown that the paroxysms of malarial patients occur at the same time as the sporulation of the parasites, took the first step (1889) toward establishing the relationship between the varieties of the parasite and the various forms of malarial fever. Golgi's discovery of the coincidence between the malarial paroxysms of the patient and the sporulation of Plasmodia was confirmed by Dr. (after

wards Sir William) Osler, while the task of determining the exact casual relationship between pernicious, tertian, and quartan fever on the one hand, and P. falciparum, P. vivax, and P. malaria on the other hand, was immediately completed by Marchiafava and Celli.

In 1886 Dr. G. M. Sternberg directed the attention of the medical profession in the United States to the views of Laveran concerning the etiology of malaria, and these soon gained support from the investigations of Councilman, Abbott, Thayer, and others, including Osler. As early as 1883 Dr. A. F. A. King had put forward as worthy of observation and experiment the supposition that mosquitoes (rather than marsh vapor) are the source of malarial infection. In 1889 Theobald Smith demonstrated that Texas fever is caused in cattle by a hæmatozoan parasite, later (1893) shown to be carried by an insect. It remained for Manson to formulate a definite verifiable hypothesis concerning the relation of the mosquito to the malaria parasite. With his studies of filaria in mind he proceeded on the supposition that the protozoa, after undergoing sexual reproduction, complete their life-cycle in the body of an insect host. Laveran had observed in the blood of malarial patients withdrawn from the circulation that some of the gametocytes put forth motile filaments. These processes, mistaken by Manson for