SECTION B.— CHEMISTRY. 



RESEARCHES IN CHEMOTHERAPY 



ADDRESS BY 



Dr. F. L. PYMAN, F.R.S., 



PRESIDENT OF THE SECTION. 



Chemotherapy may be regarded as the treatment of disease by chemical 

 substances, which have been shown by biological methods to be relatively 

 much more toxic to pathogenic organisms than to human or other animal 

 hosts. 



Chemotherapy was developed by Paul Ehrlich, and its most out- 

 standing achievement has been the introduction of the arsenic group of 

 spirochaeticides. Very early on, Ehrlich noticed that when certain dye- 

 stuffs were injected into the living animal, they selected certain tissues 

 which were intensely stained, whilst others were left practically free from 

 colour, and as long ago as 1891, he observed that the malarial parasite 

 was strongly stained by methylene blue and thus differentiated from the 

 tissue of the host. It then occurred to him that it might be possible to 

 discover dyestuffs or other drugs whose chemical affinity for disease 

 organisms was so great that the organism might be killed without damage 

 to the tissues of the host. 



Successful results were obtained in the laboratory with dyes such as 

 methylene blue, Trypan-red, and Trypan-blue, but the practical value 

 of these dyes has been slight. 



In the course of his studies Ehrlich soon found it necessary to find 

 some means of expressing the chemotherapeutic activity of compounds 

 for purposes of comparison. He therefore determined for each new 

 substance the ratio of the minimum curative dose to the maximum 

 tolerated dose, which he called the Chemotherapeutic Index. 



The ideal compound would obviously be the one which would destroy 

 the parasitic agents of disease without in any way injuring the cells of 

 the body. Such a compound has yet to be discovered, for every known 

 substance which is toxic to parasites is also toxic to a greater or lesser 

 extent to body tissues. For practical purposes the chemotherapeutic 

 index should be as favourable as possible. 



Chemotherapeutic research postulates co-operation between clinicians, 

 biologists and chemists. The first step is the discovery by the biologist 

 in co-operation with the clinician that some parasite is responsible for a 

 given disease. Then methods must be found by which the parasite can 

 be isolated, cultivated and studied. Sometimes this can be done in the 

 test-tube, as in the case of the researches on bactericides and amcebicides, 



