TREATMENT OF SLEEPING SICKNESS 105 



cific poisons against the Gambian trypanosome, having a decided 

 effect in a few hours. The most effective method for the use of 

 arsenic is to inject it into the muscles in the form of salvarsan or 

 atoxyl, the latter being a compound which is more frequently and 

 effectively used to kill trypanosomes in the blood. It is injected 

 as a weak solution, the injection being repeated every few days 

 for a period of many months, even though all symptoms of the 

 disease may long since have disappeared. A serious objection 

 to the use of atoxyl is the slight degree of toleration which many 

 people have for it, and the serious effects which it frequently has 

 on the optic nerve, often causing blindness, and on the digestive 

 apparatus. 



A still more effective drug for destrojdng trypanosomes in 

 blood and lymph is tartar emetic, an antimony compound. It 

 is injected in very weak solutions directly into the veins, care being 

 taken not to allow any of it to escape into the muscles or con- 

 nective tissues since it is excessively irritating to these tissues. 

 Usually a high fever follows the administration of either this 

 drug or atoxyl, probably due to the toxic substances liberated 

 in the blood from the dead bodies of the trypanosomes. 



The chief difficulty in the use of either 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 



