Page:Popular Science Monthly Volume 76.djvu/343

Rh from the pigmented cells found in the stomach of the mosquito to the rod-shaped bodies in the salivary glands. He then exposed birds free from parasites to the bites of such infected mosquitoes, and fourteen days later these birds had parasites in their blood. In this manner were demonstrated the development of the malarial parasites in the mosquito, the mode by which they were transmitted and the fact that not every kind of mosquito will transmit the microscopic animal which causes the disease. Although it was in birds that the complete life-cycle of the organism was first followed, the pigmented cells which were a clue to the discovery were first seen in man.

A few months after his appointment at Liverpool, Professor Ross left England for Sierra Leone, Africa, on the first of those expeditions which have made the school famous. The purpose of the expedition was to study still further the subject of malaria, but this time in the human being. Mr. Austen, of the British Museum, accompanied him for the purpose of collecting and studying the various kinds of mosquitoes and noxious insects.

This first malarial expedition was followed by many other such expeditions; and the value of the four measures for the prevention of malaria advocated by Professor Ross may be seen in the results that followed the expedition to Ismailia in 1902. Ismailia is a town of under 6,000 inhabitants, situated close to the Suez Canal and controlled by the Suez Canal Company. The number of cases there rose from 300 in 1877 to 2,250 in 1900. An active campaign of first detecting, isolating and treating the sick; second, segregating the healthy; third, mechanically protecting the well from mosquitoes; and fourth, reducing the number of mosquitoes by drainage or other treatment of their breeding places, begun in 1902, reduced the number of cases from 1548 to 37 in 1905; and all the old cases of 1905 were cases of relapse.

In 1902, Professor Ross received a Nobel prize for his researches on malaria. In 1906, he went on a malaria expedition to Lake Copais, Greece, and in 1907, he was sent at the request of the Government of Mauritius to give advice on the prevention of malaria in that island of the Indian Ocean. It will thus be seen that the work of Professor Ross is not only of scientific value, but thoroughly practical as well.

Another malady closely associated with malaria is blackwater fever. The classical description of this disease has been written by another teacher of this school, Dr. Stephens, who, next to Professor Ross, has done so much to spread a knowledge of malaria and tropical medicine. In 1907, Dr. Nierenstein, a chemist of the school, discovered certain etiological factors in this malady; and in July of the same year, the nineteenth expedition was sent to Africa to study blackwater fever.

A second disease conveyed by mosquitoes is yellow fever, which is distinctly American in origin. Found by Cortez in Mexico and