236 EXPEKIMEXTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



duces symptoms opposite to those of the disease ; and then we 

 can readily see tlie possibility of the morbid changes being 

 counteracted by the action of the drug and benefit resulting 

 from the treatment. For example, large doses of digitalis 

 render the ]>ulse extremely rapid, but moderate ones slow it.*^ 

 In this instance its moderate administration when there is a 

 rapid pulse is homoeopathic treatment, and this has sometimes 

 been beneficial. But it is not proved that all drugs have an 

 opposite action in large and small doses, and homoeopathy, 

 therefore, cannot be accepted as an universal rule of practice. 



Constitution and Idiosyncrasy. — Variations in the action of a 

 drug cannot be entirely explained, however, by the varying 

 amount in wdiich it may be actually present in the circulation 

 and acting on the body. Another modifying element of great 

 power is constitution. In animals generally we have certain 

 motor arrangements in the bones and muscles, regulating 

 arrangements in the nervous system, and yet other arrangements 

 in the circulatory system for supplying them with the material 

 necessary for the performance of their functions. But the p.irts 

 which enter into each of these are not equally developed in all 

 animals ; in some one part preponderates ; in others, another. 

 Even in animals of different species, and in individuals of the 

 same species where the relative size of organs seems the same, 

 differences nevertheless exist ; and the presence of a few cells 

 more or less in a ganglion, and a few fibres more or less in a 

 nerve, may alter to a very great extent the action of any sub- 

 stance on the organism. When a medicine given to one person 

 produces an effect slightly differing from that Avhich it gener- 

 ally causes, the difference is said to be due to constitution; 

 when its difference is great, it is said to be due to idiosyncrasy. 

 Now, these effects may be merely due to differences in absorp- 

 tion and excretion, as has been already explained, or to tlie 

 different relative development of other parts, especially parts of 

 the nervous system. It is easy to understand the altered effect 

 which may be thus produced, and to perceive the ambiguity of 

 such terms as " nervous stimulant," wdien we recollect that 



* Vide Traube, Med. Centr. Ztg., vol. xxx, p. Ui, 18G1, and Erunton On 

 Digitalis, p. 21 (^oide antea, p. 47). 



