58 SECTIONAL ADDRESSES 



to which I shall refer in detail later. In other cases, the particular disease, 

 or one closely related to it, may be induced and studied in animals. 



Schulemann (1932) has traced the stages in the development of a 

 laboratory method for evaluating antimalarial drugs in the following 

 words : ' In 1880 Laveran discovered the malarial parasite, and in 1891 

 Grassi and Feletti found in birds a parasite similar to that of human 

 malaria. In 1895, Ross, stimulated and directed by Manson, discovered 

 the role played by the mosquito in transmitting the disease. How bird 

 malaria might be used for the study of malarial treatment in man was 

 investigated by Kopanaris and the brothers Sergent, but it was not till 

 1924 that a satisfactory technique was evolved ' by Roehl, who * worked 

 out a method of using canaries for experiments on lines closely approach- 

 ing the conditions of practical therapy, so that it was possible to try out 

 and assess in the laboratory many groups of drugs.' 



On the chemical side, researches in chemotherapy start from the 

 discovery that some drug, whose constitution is wholly or partly known, 

 is of clinical benefit in a given disease or is toxic to certain organisms. 

 Once some knowledge of the chemical constitution of the drug has been 

 obtained, substances more or less closely related to it can be synthesised 

 and tested for their chemotherapeutic properties. 



Traditional knowledge of the value of cinchona bark in malaria, 

 followed by the isolation of quinine and the associated alkaloids, the 

 recognition that the medicinal value of the bark was due to these, and the 

 determination of their chemical constitutions, made possible the chemo- 

 therapeutic researches which led to the discovery of plasmoquin and 

 atebrin. 



Bactericides. 



The introduction of phenol or carbolic acid for the prevention of sepsis 

 by Lister in 1867 formed the starting-point in research on bactericides. 

 A very large number of derivatives of phenol have since been made and 

 tested for their bactericidal properties. The efl^ect of substituting one 

 or more alkyl groups in the benzene ring has been studied, and it has 

 long been known that many alkyl-phenols exceed phenol itself in 

 bactericidal value. One method of determining the phenol coefficient 

 of bactericides is the Rideal Walker test, comparing their efficiency with 

 that of phenol in destroying B. typhosus. By this test the cresols — methyl- 

 phenols — have phenol coefficients of 2 to 2-5, whilst thymol — a 

 methylwopropylphenol — has a phenol coefficient of about 25. 



In recent years, systematic studies have been made of several homo- 

 logous series of phenols. An early example of the investigation of a 

 homologous series was made in another field by Morgenroth and his 

 collaborators (1911-1917). They studied the homologous series of 

 alkylhydrocupreines, and showed that peak activity was obtained at the 

 ethyl member (optoquin) for pneumococci, and at isooctyl (vuzin) for 

 B. diphtheriee. In clinical use optoquin proved to be unsatisfactory for 

 the treatment of pneumonia, but vuzin was used in the treatment of 

 wounds. 



American chemists demonstrated the profound effect of the length of 



