818 



SCIENCE 



[N. S. Vol. XXXII. No. 832 



in severe cases of this disease. It is diifi- 

 cult to say, however, whether it is a true 

 curative agent, since the disease is apt to 

 run a prolonged and insidious course, and 

 a long time, therefore, is required to judge 

 whether a patient is actually cured. Much 

 also depends upon the virulence of the 

 parasite; thus, for instance, Ehrlich, who 

 experimented with a particularly virulent 

 strain of nagana trypanosoma, found it 

 more refractory to atoxyl than other forms 

 of this parasite. In this series of experi- 

 ments he made the very interesting obser- 

 vation that acetylparaaminophenyl arsinic 

 acid acted even better than atoxyl and 

 proved less poisonous to mice. On the 

 other hand, this substance was far more 

 poisonous in other animals, such as guinea 

 pigs or horses. Curious to say, the admin- 

 istration of acetylparaamidophenyl arsinic 

 acid made "dancing mice" of the treated 

 animals. 



From these experiments the conclusion 

 may be drawn that every species of animal 

 and every form of trypanosoma would 

 probably require some special curative 

 agent, a fact which naturally makes the 

 treatment of all the different trj'panosoma 

 affections far more difficult. 



Like the parasite of relapsing fever, the 

 trypanosoma may disappear from the 

 blood under continued treatment, only to 

 reappear at a later period when the dis- 

 ease is regarded as cured. There is thus a 

 period of what may be termed immunity 

 which may be of varying duration. Ehr- 

 lich found, for instance, that when mice 

 inoculated with the trypanosoma of caderas 

 were treated with trypanred the parasites 

 apparently vanished completely from the 

 blood, but in the course of twenty to thirty 

 days reappeared and speedily caused 

 death unless another course of treatment 

 was substituted. Mesnil and Nicolle ob- 

 served such a reappearance of the parasite 



after an interval of freedom of three to 

 five months. It wiU be readily seen, 

 therefore, that the disappearance of the 

 trypanosoma in a case of sleeping sickness 

 does not by any means signify that the 

 patient is definitely cured. The blood has 

 to be reexamined from time to time over 

 long periods until an actual cure is as- 

 sured. But even these tests are not abso- 

 lutely positive, for it has been repeatedly 

 shown that when the trypanosoma is no 

 longer present in the blood and cerebro- 

 spinal fluid it may still be found in the 

 bone marrow. Another curious circum- 

 stance is that an infected animal or human 

 being apparently rid of the parasite and 

 entirely well, may still be capable of trans- 

 mitting the disease to others. 



A further obstacle in the treatment of 

 sleeping sickness and other trypanosoma 

 affections is that the parasites after a time 

 acquire a power of resisting the remedy 

 used for their destruction. This is some- 

 what like the tolerance to drugs acquired 

 by human beings. Thus, for instance, it 

 has been found that the nagana trypano- 

 soma when inoculated into mice could be 

 made to disappear under treatment with 

 fuchsin for a number of weeks, and upon 

 their return could again be made to vanish 

 by the same treatment. Finally, however, 

 a time comes when this can no longer be 

 accomplished. Evidently some change has 

 taken place in the trypanosomes which en- 

 ables them to resist what had previously 

 proved destructive. 



Browning thus has obtained strains of 

 trypanosoma whicjh have become resistant 

 to the two groups of atoxyl, and to 

 trypanblue, trypanred, etc., or even to 

 three of these groups of substances. 

 His researches show that this quality 

 if once acquired is quite persistent and 

 may even be transmitted to the progeny 

 of the trypanosome. He believes that 



