Deoembee 9, 1910] 



SCIENCE 



811 



supplied a specific remedy, quinin, long 

 before the discovery of the plasmodium. 

 On the other hand, the study of the life 

 history of this organism and the demon- 

 stration of its transmission through the 

 bite of the mosquito, have rendered it pos- 

 sible to devise means for malarial prophy- 

 laxis. In the case of syphilis clinical 

 experience dui'ing many centuries has dem- 

 onstrated the value of mercury in control- 

 ling the manifestations of this disease, but 

 although vaunted as a specific, this remedy 

 can not be regarded a true curative agent, 

 since it has failed to prevent recurrences 

 from taking place, sometimes even after 

 long periods. 



One of the most malignant of this group 

 of protozoal parasites is the trypanosoma, 

 the cause of the dreaded sleeping sickness 

 and of various diseases in horses and cat- 

 tle, whose ravages, especially in the 

 African colonies of England and Germany, 

 make it one of the worst pests with which 

 mankind is afflicted. 



A brief description of these parasites 

 will, perhaps, prove instructive. In the 

 first place it must be noted that the try- 

 panosoma has been found in the blood of 

 many animals, both cold- and warm- 

 blooded, and that some varieties of this 

 parasite appear to be perfectly harmless. 

 Those which are of particular interest, be- 

 cause of their virulence, are as follows: 

 (1) Trypanosoma evansi, discovered by 

 Evans more than twenty-five years ago, 

 which is the cause of surra, a destructive 

 disease of hoi"ses, camels, cattle and dogs 

 prevailing in India as well as in other 

 parts of Asia, and in the Philippines and 

 Africa. (2) Trypanosoma brucei, discov- 

 ered in 1894 by Bruce, which causes the 

 very fatal nagana or tsetse fly disease of 

 Africa in various domestic animals (horses, 

 mules, dogs, cats, etc.), but like the pre- 

 ceding does not attack man. (3) Try- 



panosoma equiperdum, the cause of dou- 

 rine, a disease affecting horses, but, unlike 

 the above, found outside of tropical coun- 

 tries, particularly on the shores of the 

 Mediterranean. (4) Trypanosoma equi- 

 num, the cause of mal de caderas, occur- 

 ring almost entirely among horses in 

 South America. (5) Trypanosoma Gam- 

 biense, the most important of this group, 

 first shown to be the cause of human try- 

 panosomiasis by Castellani in 1902. (6) 

 Parasite of mbori, a disease of camels in 

 the Sudan, especially in Timbuctoo. 



Trypanosomes, while differing more or 

 less in their special characteristics, have 

 in common a worm-like body and are 

 flagellated, that is, provided with a mem- 

 branous sheath (undulating membrane) 

 terminating in a slender whip-like process 

 designed for locomotion. They are much 

 larger than bacteria and can be seen with 

 a comparatively low power of the micro- 

 scope swiftly darting between the blood 

 cells, brushing them aside, but not pene- 

 trating them like the parasite of malaria, 

 the Plasmodium. One of the most remark- 

 able features in their life history is their 

 manner of transmission. While infection 

 with bacteria takes place directly, as 

 through the air, food, water, or through a 

 wound, the trypanosoma, like the parasite 

 of malaria, requires an intermediary or 

 complementary host, usually some blood- 

 sucking insect, as the Indian horse fly or 

 the tsetse fly of Africa. In the act of 

 sucking an infected person or animal the 

 insect draws up the parasite with the blood 

 and carries it about in his proboscis, and 

 later again injects it in biting another in- 

 dividual. While in the case of the Plas- 

 modium the parasite undergoes certain 

 changes in the body of the insect, this has 

 not been shown to occur with trypanosome, 

 so that it is commonly believed that the 



