RESEARCH IN MEDICINE 121 



and Wassermann have shown the possibility of preparing specific cellular 

 poisons for cancer analogous to those used in curing protozoan diseases. 

 The final clue which will unravel the mystery of this complex disease 

 would not appear to be as yet fully in hand, and yet I think no one of 

 those most conversant with the problem would be surprised to find 

 to-morrow that it has been discovered and that cancer was curable. 



Protozoology. — It is of interest that about the year 1890, when bac- 

 teriologists ceased to announce discoveries with their accustomed regu- 

 larity, owing to the fact that all readily recognized pathologenic bac- 

 teria had been discovered, the systematic study of protozoa began and 

 some of the single-cell forms of life in the animal kingdom soon took a 

 place as disease-producers alongside the corresponding form of the vege- 

 table kingdom. Until this time, protozoa had been found in only two 

 diseases of man, dysentery and malaria. In the year 1890 appeared the 

 first books on the subject of protozoa as causes of disease, a small vol- 

 ume of one hundred pages by L. Pfeiffer, followed in the next year by 

 Doflein's more extensive discussion of the same subject from the 

 broader biological point of view. The bacteriologists of the preceding 

 decade had by their efforts limited the number of diseases in which a 

 bacterial etiology could be readily shown and it was natural, therefore, 

 that the attention of investigators turned to the study of other micro- 

 organisms as factors in the production of disease. The careful tech- 

 nique of the bacteriologist had shown the methods to be used in the 

 study of etiology, and, undoubtedly, the publications of Pfeiffer and 

 Doflein stimulated general interest in the search for pathogenic pro- 

 tozoa. However this may be, it is a matter of record that in 1890 

 " only two human diseases were suspected of being caused by protozoa. 

 . . . To-day more than fifteen are known or suspected to be of pro- 

 tozoan origin" (Calkins). 



In the discussion of bacteriology I have referred to Leeuwenhoek as 

 the first to see bacteria; he was likewise the first to see protozoa (1675). 

 Two hundred years later, Biitschli (1875) offered conclusive evidence 

 of the unicellular nature of these minute forms of animal life. In the 

 intervening period, however, owing largely to the work of 0. F. Muller 

 (1786), Ehrenberg (1833-38) and Dujardin (1835-41), many forms 

 had been removed from the " chaos animalculse," the name under which 

 Cuvier had classified them and their structure had been studied by 

 Siebold (1845) and Max Schultze (1863). In this later period also 

 several forms now familiar to us as occasional parasites of man had 

 been described; as the Trichomonas vaginalis (Donne in 1837), the 

 Cercomonas liominis (Davaine, 1857), the Balantidium coli (Malm- 

 sten, 1857) and the Lamblia intestinalis (Lambl, 1859). 



The first parasitic protozoon, however, to be definitely associated 



VOL. LXXXI. — 9. 



