TREATMENT OF SLEEPING SICKNESS 105 



in the form of atoxyl or salvarsan, injected intramuscularly, or 

 antimony in the form of tartar emetic, injected intravenously. 

 Atoxyl is injected in weak solution, the doses being repeated 

 every few days for a period of many months, even long after the 

 symptoms of the disease have disappeared. A serious objection 

 to atoxyl is the slight tolerance which many people have for it, 

 and its serious effects on the optic nerve and digestive apparatus. 

 Tartar emetic is also injected in weak solutions, care being taken 

 not to allow it to escape into the muscles or connective tissues, 

 to which it is very irritating. Usually a high fever follows the 

 administration of either drug, probably due to toxic substances 

 liberated from dead trypanosomes. Recently the Rockefeller 

 Institute has produced a new arsenic compound, tryparsamide, 

 which promises to be more valuable than any other drug yet tried. 

 It is very soluble in water, can be given either intramuscularly 

 or intravenously, produces practically no untoward effects, ef- 

 fects very rapid destruction of the parasites in the blood, brings 

 about very marked improvement in the condition of the spinal 

 fluid in advanced cases, and results in remarkable general ben- 

 eficial effects. 



The chief difficulty in the use of any of these drugs is that the 

 trypanosomes tend to build up a tolerance for them, in much 

 the same way that a man may build up a tolerance for opium 

 or other drugs. This tolerance is hereditary and" gives rise to 

 " arsenic-fast " or " antimony-fast " strains of trypanosomes. 

 In such cases the parasites cannot be destroyed. It is an inter- 

 esting fact that in at least one species of trypanosome, T. lewisi 

 of rats and mice, and probably others as well, when strains im- 

 mune to atoxyl are passed through their intermediate host, a 

 louse, where they presumably undergo sexual reproduction or 

 some process which takes its place, the tolerance is entirely lost. 

 Thus the sexual process at a stroke eliminates acquired charac- 

 ters which have been maintained through thousands of asexual 

 generations in passages from mouse to mouse or from rat to rat. 

 This fact, if invariably true, is of considerable importance in 

 the outlook for the treatment of sleeping sickness, since it would 

 prevent what would otherwise inevitably happen, the evolution 

 of a permanent strain of trypanosomes immune to both arsenic 

 and antimony. The fact that parasites resistant to arsenic may 

 not be resistant to antimony, and vice versa, makes it advisable 



