1 8 THE HISTORY OF TROPICAL MEDICINE 



mosquito is that it paved the way for Ross's discovery of the spread of malaria 

 by a similar agency. 



It is quite impossible here to give even a reasonable list of the workers on 

 this important branch of causation, but references to their discoveries will be 

 found later in this book. 



Protozoology. — Protozoa were recognized by Leeuwenhoek in 

 1675, and the first life-history of a protozoon (a vorticella) was 

 worked out by Trembley in 1744-1747. 



Among the protozoa parasitic in human beings, one of the first 

 to be discovered was Balantidium coli, found by Malmsten of Stock- 

 holm in the year 1856, and now known to be often associated with 

 a chronic catarrh and ulceration of the large bowel. Lamblia 

 intestinalis, discovered by Lambl in 1859, Trichomonas hominis, 

 found by Davaine in 1864, are considered by many authors (Ebstein, 

 etc.) to be the cause of certain cases of diarrhoea. 



In 1875 an amoeba was found by Losch in St. Petersburg, in a 

 peasant who suffered from an ulcerative inflammation of the large 

 intestine, and Sonsino in Cairo also described the finding of large 

 numbers of amoebae in the intestinal mucus of a child who had died 

 of dysentery. Other observers, however — e.g., Grassi, Celli, and 

 Cunningham — found amoebae in persons whose health had under- 

 gone no change. Kruse and Pasquale first suggested that there 

 might be two species of amoebae, one pathogenic, the other harm- 

 less. Later Schaudinn showed that there were two kinds of amoebae 

 affecting man — viz.. Entamoeba coli, which was non-pathogenic; 

 and Entamoeba histolytica, described by himself, which was the cause 

 of a certain kind of dysentery (amoebic dysentery) and of the abscess 

 of the liver which at times followed it. 



The discovery which has had the greatest influence on tropical 

 medicine was that of the parasite of malarial fever by Laveran on 

 November 6, 1880. True, this had to some extent been fore- 

 shadowed by Merkel in 1847, and Virchow in 1848, both of whom 

 saw, and the latter figured, protoplasmic masses and pigment. 

 Still, the entire credit for this great discovery is due to Laveran, 

 for the others failed to recognize the parasitic nature of the forms 

 they saw. The development of our knowledge concerning this 

 parasite is due to the valuable researches of Golgi, Marchiafava, 

 Celli, Bignami, and many others. Of great importance was Golgi's 

 discovery of the plurality of species of the malarial parasite. 

 Laveran's discovery and the work of his successors left, however, a 

 great gap in the history of the parasite. They described lucidly 

 its life-history in the human being, but could not explain how man 

 became infected. 



Sir Patrick Manson, reasoning on his work on the mosquito and 

 filaria, suggested that there might be a stage of the development of 

 the parasite in the mosquito. Working on Hanson's theory, Ross, 

 at that time in the Indian Medical Service, after years of patient 

 hard work, was able to trace the full development of a bird's para- 

 site in Culex, and partially that of the human parasite in the Ano- 



