224 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



injure the part that its function is abolished, and no action 

 exerted upon it can produce any effect. But it is impossible to 

 do tliis in man, and so ^Ye must have recourse to the lower 

 animals, in which we can produce at will the conditions 

 we desire. Althougli the administration of a medicine to a 

 patient is really an experiment, we vary the conditions in 

 which it acts to so much greater extent in animals that it is 

 convenient to call the latter mode of investigation tlie experi- 

 mental mctliod, and the former that of clinical observation. 



Now pathology and pharmacology may go on hand in hand 

 both in teaching and study, but they must always be preceded by 

 pliysiology ; fo ', unless we know the processes which take place 

 in the healthy organism, it is impossible to understand the 

 changes they undergo in disease, or the effect of drugs upon 

 them. I will, therefore, here say a few words regarding the 

 processes in which life consists, before proceeding to speak of 

 the mode in which they moy be modified by the action of 

 remedies. 



Life. — We meet with life only in certain bodies composed of 

 carbon combined in a very complicated manner with oxygen, 

 liydrogen, and nitrogen ; and it may, generally speaking, be said 

 to be the power which these bodies possess of assimilating to 

 themselves other substances, of decomposing them, and of 

 evolving energy, which is shown in active motion, active 

 growth, &c. Evolution of energy in this way is tlie distinguish- 

 ing mark of life. When we look at a grain of wheat, an egg, or 

 a dried wheel-animalcule, we are unable to say whether or not 

 it is alive ; it is only when it begins to evolve energy, either by 

 moulding other substances into conformity with its own con- 

 stitution in active growth, as in the seed or egg, or by active 

 motion, as in the animalcide, that we are able to decide the 

 question. We cannot say how these bodies originally came to 

 possess their complicated constitution and wonderful powers ; 

 but the evolution of energy by which we recognise the continued 

 presence of life seems to be more intimately associated with 

 chemical affinity than with other forms of energy, such as light, 

 heat, or electricity. All these forms of energy modify the pro- 

 cesses wdiich occur in living beings, both those which are 



