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SCIENCE 



[N. S. Vol. XXXIV. No. 



ties. The cause of yellow fever, however, 

 is still unknown; when discovered, the 

 cure for the disease will surely follow just 

 as its prevention followed the discovery 

 of its mode of transmission. 



After the malaria problems were cleared 

 up, discoveries of other protozoan diseases 

 followed in quick succession. Kala azar, 

 dum dum fever, oriental sore and allied 

 diseases of the far east, were found by 

 Leishman, Donovan, Wright, Christophers, 

 Patton and others, to be due to a flagel- 

 lated protozoon of the genus Herpeto- 

 ■monas, and transmitted by bed bugs. 



Sleeping sickness, the great scourge of 

 central Africa, was hunted down by the 

 indefatigable David Bruce in 1903, who 

 showed that it is transmitted by a tse tse 

 fly, Glossina palpalis. This discovery fol- 

 lowed his brilliant researches of 1894-97 

 when he traced the cattle disease called 

 "nagana" and the "tse tse fly disease" of 

 cattle to the same protozoon — Trypano- 

 soma hriicei — and showed that a tse tse 

 fly — Glossina morsitans — is the intermedi- 

 ate host. The final observations on human 

 sleeping sickness were possible through 

 the earlier discoveries by Lewis in 1879 on 

 a trypanosome of the rat; by Forde (1901) 

 and Dutton (1902) of a trypanosome in 

 victims of Gambia fever which was re- 

 garded up to that time as distinct from 

 sleeping sickness. This organism was 

 named by Dutton Trypanosoma gambi- 

 ense. Also, in 1903, Castellani discovered 

 a trypanosome in the cerebrospinal fluid 

 of victims of sleeping sickness and named 

 it Trypanosoma ugandense. Bruce showed 

 that the trypanosomes of the two diseases 

 are the same and that Gambia fever is the 

 initial phase of the fatal disease. 



Time does not permit even the naming 

 of other species of trypanosomes found in 

 warm- and cold-blooded animals; nor of 

 the many researches that have resulted in 



the discovery of intermediate hosts 

 amongst leeches, flies and lice. Much has 

 certainly been accomplished, but there 

 still remains a great and undeveloped field 

 for research in the life histories of the 

 various species. 



Perhaps the most spectacular discovery 

 in connection with protozoa and disease 

 was that of Schaudinn in 1905, when in a 

 short publication he announced the discov- 

 ery of spirochastes in syphilitic lesions. 

 This modest little paper of four or five 

 pages has been the inspiration of thou- 

 sands of titles, most of which have added 

 little or nothing to Schaudinn 's original 

 work, the majority dealing with tech- 

 nical methods, a few with morphological 

 changes and the life history, and a few, 

 notably Robert Koch's, with treatment. 

 Other spirochete diseases, such as yaws or 

 frambesia, human relapsing fever and 

 tick fever, or diseases of cattle and poul- 

 try, have been shown to be transmitted by 

 ticks of one species or other, but Tre- 

 ponema pallidum, as Schaudinn finally 

 called the spirochsete in syphilis, is appar- 

 ently transmitted solely by contact. 



One of my students this spring made the 

 comment that most of the references I 

 had given in connection with pathogenic 

 protozoa seemed to fall within the period 

 of 1900-05. The observation was entirely 

 correct and the fact is undeniable that the 

 last five years have given little of value in 

 this branch of protozoology, while in the 

 preceding five-year period not only were 

 the majority of protozoan diseases dis- 

 covered and their means of transmission 

 established, but that period gave us Mes- 

 nil and Mouton's method of cultivating 

 parasitic amoeba on artificial media, and 

 the brilliant researches of Novy and Mac- 

 Neal resulting in an entirely new method 

 for the study of parasitic flagellates. 

 Since that period few new discoveries 



