RESISTANCE TO DRUGS. 119 



isms is what makes the second attack possible, and 

 that this might go indefinitely were it not that the 

 host eventually responds by the production of 

 such a quantity of germicidal substances that the 

 spirilla are finally destroyed. We may suppose 

 that the conditions are not very different in syph- 

 ilis and in some of the chronic protozoic infections, 

 as trypanosomiasis and piroplasmosis ; in all these 

 diseases specific antibodies are produced during the 

 course of infection, and there is good reason to 

 believe that some of these are germicidal in charac- 

 ter. This is certainly true in regard to piroplasmo- 

 sis and trypanosomiasis, yet the organisms persist 

 in the blood and tissues of the host for a long 

 period. It seems that they must have become 

 adapted to the presence of these germicidal sub- 

 stances. That virulence is not lost as a consequence 

 of this adaptation is shown by the fact that the 

 blood when it is injected into a fresh animal repro- 

 duces a typical acute attack. 



It is noteworthy that a similar resistance to cer- Acquired 

 tain drugs can be induced in trypanosomes when 

 infected animals are given repeated injections of 

 these preparatoins. If a sufficient quantity of one 

 of these drugs (atoxyl, fuchsin, trypan-red, etc.) 

 is given to an infected animal, a complete cure, 

 with sterilization of the body, may be obtained. In 

 the event, however, that an insufficient quantity 

 of the drug is administered, the organisms when 

 injected into a subsequent animal may be entirely 

 indifferent to the presence of the drug, which, con- 

 sequently, has lost its therapeutic value against 

 this strain. It may be necessary to repeat this 

 process through many passages before a high degree 

 of drug resistance is obtained, but when once estab- 



