168 SECTIONAL ADDRESSES. 



their output of work was constant. We found that the administration 

 of a dose of caffeine dissolved in water one hour before the experiment 

 greatly increased the output of work for that day. This was repeated 

 on several occasions, always with the same result, and we naturally 

 regarded the effect as due to the caffeine. This, however, was not the 

 case : the effect was due to the ritual of taking a drug ; the drug day 

 assumed an enhanced importance in the mind of the operator and the 

 mental effect sometimes referred to as suggestion was principally respon- 

 sible. We had no difficulty in showing that water made bitter with a 

 trace of quassia or other simple bitter had a similar effect. 



Few, if any, experiments made on man without the most careful 

 controls are of any real value. Properly controlled experiments have 

 been made, however, with many substances. Precise experiments, for 

 example, have been made both in Germany and America with bromides 

 in epilepsy. In these experiments half the epileptics were given potas- 

 sium chloride and the other half sodium bromide ; after several weeks' 

 use the bromide had decreased the number of attacks, whilst the chloride 

 had no distinct action. 



Chemo-Therapy. 



At one time hopes ran high that the chemical structure of the molecule 

 might indicate pharmacological action. During the last fifty years many 

 laborious researches have been conducted with this object ; to modify 

 the molecule that it may conform to some required action. But the 

 mystery remains as mighty as ever. It is most probable that subtle 

 energy factors binding the molecule — factors not displayed in a formula — 

 control the action ; certain it is that drug action is not determined 

 directly by chemical combination with body constituents, but rather by 

 delicate physical processes such as those of adsorption, solution, and surface 

 tension. Chemists have as yet not even determined the requirements of 

 the molecule for the production of colour sensation. On the other hand, 

 slight alteration of a molecule already complicated and with a known 

 action has led to the production of many useful compounds, and not 

 infrequently we may foresee the type of action which will occur under 

 such special conditions. Considerations of this nature have led to the 

 synthesis of the new local anaesthetics, antiseptics, antipyretics, diuretics, 

 tropeines and other useful substances. 



But chemistry has taken yet a further step in its assistance given to 

 medicine in the development of that branch of science to which the name 

 chemo-therapy has been given. Ehrlich noticed that colouring matters 

 injected into the living organism had a selective affinity for certain cells, 

 and he believed that it might be possible by making use of this property 

 to select suitable substances which would destroy the causal agents of 

 disease, parasites and microbes, and leave the tissues of the host 

 uninfluenced. 



Parasites causing disease in man may be crudely divided into worms, 

 protozoa, and bacteria. Chemo-therapy, that is specific therapy of infec- 

 tious disease, has had marked success in curing disease due to parasites 

 in the first and second of these groups ; these diseases are found mainly 

 in the tropics. It has obtained much less success in the third group. 



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