126 THE POPULAR SCIENCE MONTHLY 



injection was repeated at intervals, the period of disappearance of the 

 trypanosome would gradually shorten until finally the drug would have 

 no effect on the infecting organism ; in other words, a strain of trypano- 

 somes had been developed which were resistant, immunized as it were, 

 to trypan red and this resistance could be transmitted through many 

 generations. Also, it was found that trypan red was a curative agent 

 only for the infection in mice; on the trypanosome diseases of larger 

 animals, as horses and cattle, it had no curative effect. However, the 

 experience with trypan-red pointed the way to a solution of the diffi- 

 culty; either a drug must be found which by a single injection would 

 kill every parasite, or several different drugs must be used, which, act- 

 ing on the same parasite, and thus allowing a combination treatment, 

 would lead to a cure without the danger, to the host, of a single massive 

 dose. It is impossible in the scope of these lectures to follow in detail 

 Ehriich's work or to go into the complicated chemistry of the substances 

 used. It must suffice to say that as the work went on, Ehrlich and 

 Weinberg found a substitution produced of trypan-red, amidotrypan-red, 

 which destroyed the virulent parasite of nagana, the tse-tse fly disease, 

 and that Mesnil and Nicolle, using the blue and violet azo-dyestuffs, 

 prepared a trypan blue and trypan violet which caused the disappear- 

 ance of the parasites of nagana, surra and mal de Caderas. 



Another line of progress was through various combinations of anilin 

 with arsenic. Before Ehrlich entered this field, Bruce had found 

 arsenic to be a drug of value in treating the trypanosomiasis of horses 

 (surra) and Thomas had found that atoxyl, a combination of arsenic 

 and anilin, would cure a large percentage of infected animals. This 

 latter substance had also been used in the treatment of the human 

 disease, sleeping sickness. Ehrlich made a thorough study of arsenic 

 compounds, and the result was the combination, arsenophenylglycin, a 

 single dose of which absolutely and permanently cures all animals suf- 

 fering from trypanosome infection. 



At about this stage of the development of chemotherapy, Uhlen- 

 huth and Salmon published an account of the brilliant use of atoxyl in 

 the treatment of syphilis, which as we have mentioned, is due to a 

 protozoan, the spirocheta pallida. Unfortunately, as atoxyl sometimes 

 caused blindness, its use was not without danger and therefore not de- 

 sirable. So Ehrlich immediately turned his attention to the protozoan 

 diseases caused by spirilla, as chicken spirillosis, relapsing fever and 

 syphilis. His labors on these diseases constitute one of the most fas- 

 cinating of modern laboratory studies and his results are among the 

 greatest of scientific discoveries. His intimate knowledge of the con- 

 stitution of atoxyl and other arsenic preparations allowed him to pro- 

 ceed rapidly with " a great variety of substitutions, and innumerable 

 arsenic derivatives were synthetized." As human syphilis could be 



