220 DISEASES DUE TO PROTOZOA 



thickened ribbon-like edge, the undulating membrane, 

 which starts as a minute secondary nucleus at the 

 hind extremity and ends in a rather long whip-like 

 flagellum at the fore end. They range from ^T O inch 

 to -3-5-5- inch in length and they are about ^o o mc ^ 

 wide. They move by a sinuous, jerking, boring action. 

 Division takes place by longitudinal splitting, probably 

 beginning at the hind end and proceeding along the 

 undulating membrane. The true nucleus shows its 

 division late. The human trypanosoma has resisted 

 artificial cultivation until very recently, and at the 

 present time it is very difficult to cause development in 

 the laboratory. Other forms of these protozoa have 

 been grown with comparative ease. Most animals 

 may be the hosts of trypanosoma; in some there will 

 be disease, in others the organisms live as harmless 

 commensals. The modern treatment consists in using 

 an arsenic preparation called atoxyl. Numerous 

 attempts have been made to produce a serum by 

 injecting animals with trypanosoma. Sera thus 

 obtained have a slight beneficial effect upon the lower 

 animals, but have not proven of great value with 

 human beings. The injection of attenuated cultures 

 has raised the resistance of certain lower animals. 

 The fact that some resistance can be attained by 

 attempts toward the production of active and passive 

 immunity indicates that trypanosoma exert their 

 action by some poison. Whether it be in their bodies 

 or elaborated in the juices about them is not known. 

 Trichomonas. Two protozoa of a slight medical 

 importance are the Trichomonas vaginalis, with its 

 nearly related varieties, T. intestinalis and T. pulmo- 



