CHEMICAL REMEDIES 287 



biological methods have failed, and quinine remains the 

 sovereign remedy. Hence, instead of searching for a vaccine 

 or a serum in protozoal diseases, the search has been directed 

 to finding an equivalent of quinine for each. 



When fortune favours, the history of cinchona bark and 

 quinine may be recapitulated. Chance or an empirical dis- 

 covery or a tradition of unknown origin, then enriches 

 humanity with a remedy on which chemists and experimenters 

 exercise their talents. This is the history of the recent arsenical 

 remedies. 



The discovery of the microbes and the necessity of dis- 

 covering for protozoal diseases other remedies than vaccines 

 and serum, have been aided by the development of chemistry 

 itself, and especially of industrial chemistry. The great aniline- 

 dye factories have been the chief furnishers of the laboratories 

 of experimental medicine. The remedies tried have been 

 varied as the dyes are varied, and in many cases chemiotherapy 

 has been really a chromotherapy. 



The method of research consists in associating experiments 

 on the living animal with the reactions of organic chemistry. 

 A certain body endowed with a certain property is known ; the 

 molecule of this body possesses a principal nucleus on which 

 are grafted secondary atomic groups; it is found that the 

 property desired depends upon one of these groups ; this group 

 is then shifted about, varied or substituted by another group ; 

 experiment then informs us as to the properties of the 

 new compound and as to the relations between molecular 

 structure and therapeutic effect. 



Ehrlich has rendered great services to medicine by combining 

 more closely than had ever been done, the technique of the 

 chemist with the in vivo experiments of the biologist. His 

 guiding principle, which dominates his whole career and is to 

 be found in his earliest works, is the attempt to explain vital 

 actions by a similar mechanism as in the reactions of organic 

 chemistry. He has represented by stereochemical formulae the 

 reciprocal reactions of bodies of the chemical composition of 

 which we are almost entirely ignorant, the toxins and antitoxins. 



