EHRLICH'S SPECIFIC THERAPEUTICS 221 



drugs, his problem has been in each case to find a protoplasmic poison 

 of such nature that it will not injure the patient's tissues, but will steri- 

 lize his body against the parasites in one or two injections. Success in 

 finding such drugs must obviously depend upon an intimate knowledge 

 of the relation between chemical structure and pharmacodynamic action 

 and, in this obscure matter, Ehrlich has had at his fingers' ends a 

 fund of practical information that is almost unprecedented. It is 

 known that the physiological action of the organic radical in a drug 

 molecule is the same, no matter what combination it enters into, while 

 the inert parts of the molecule may alter the degree, but not the kind 

 of action. Thus the anesthetic effect of cocaine or its derivatives is 

 due to the amido-benzoic acid group in the cocaine molecule. Again 

 the most toxic compounds are those which most rapidly liberate the 

 active atom group in the molecule by decomposition, as in the case of 

 many coal-tar products. Building upon facts of this kind, Ehrlich 

 has in a surprisingly short time turned out definite effective remedies 

 like methylene blue for quartan fever, trypan red in bovine piroplas- 

 mosis (Texas fever), arsenophenylglycine for the trypanosomiases 

 (sleeping sickness in man, surra and mal de caderas in horses), dioxy- 

 diamidoarsenobenzol or " 606 " for the spirilloses (syphilis and relaps- 

 ing fever). The technical and structural details of this wonderful 

 piece of chemical research have been very thoroughly and ably de- 

 scribed in a recent number of Science by Dr. H. Schweitzer 16 to which 

 our readers may be referred. One instance of the extreme specializa- 

 tion of Ehrlich's chemotherapeutic knowledge may be quoted, his 

 theorem that effective remedies for sleeping sickness must be " tetrazo 

 colors derived from naphthalen disulpho-acids with the sulpho-groups 

 in the 3.6 position." 17 The labors involved in building up and trying 

 out several hundred of these new compounds was enormous, and in 

 order to facilitate a system of exclusion, Ehrlich utilized his discovery 

 of parasitic immunity against drugs in his device of a " cribrum 

 therapeuticum " or therapeutic sieve, which will immediately classify 

 any new chemotherapeutic substance in regard to its destructive effects 

 upon pathogenic parasites. This is accomplished by rendering differ- 

 ent parasites resistant to various drugs (e. g., fuchsine or atoxyl) 

 through many generations, until finally a " strain " or breed is pro- 

 duced that is definitely fuchsine-fast, atoxyl-fast, etc. When a new 

 drug is tried upon these different resistant strains, its pharmacody- 

 namic status can be ascertained at once. If it destroys all the resistant 

 strains it clearly belongs to a new and untried group. Ehrlich has 

 even succeeded in cultivating strains of trypanosomes each of them re- 



18 " Ehrlich's Chemotherapy — A New Science," by Dr. H. Schweitzer, Science, 

 December 9, 1910, 809-823. 

 "Ibid., 815. 



