THE STIMULI. 199 



alone,~while some are conditions as well as stimuli. Heat, for 

 example, is an essential condition for all living action, and it is 

 likewise a stimulus to all living matter, and if raised above 

 certain limits, exalts living action, causing the organism to live 

 faster an exaltation soon succeeded by a corresponding de- 

 pression. Electricity is also a stimulus to all living matter, but 

 not, as far as we know, an essential condition, while light is a 

 stimulus to only certain forms of living matter ; and magnetism 

 hardly to any, as far as we know. All stimuli, comprehending all 

 positive agents which act at all on the living matter, exalt the 

 living action in degree, and this is followed by a corresponding 

 depression if beyond the normal amount, and if the excess of 

 action caused by normal stimuli is great or long continued, 

 qualitative change as well as exhaustion of the living matter is 

 induced. But with the preternatural stimuli, such as medicines 

 and poisons, the depression after exaltation is more marked and 

 also the qualitative change, so that Trousseau calls them modi- 

 ficators. The depression and modification is often so marked as 

 to be the only thing to attract attention, and a direct paralyzing 

 effect is assumed by many authors, but Claude Bernard, as the 

 result of his long series of experiments, states that, " Every 

 substance which in large doses abolishes the property of an 

 organic element, stimulates it if given in small ones" ("Intro- 

 duction a la Medicine Experimentale ") The preternatural 

 stimuli no doubt become incorporated with the living matter in 

 the same way as the pabulum and form part of it, till decom- 

 posed or expelled, and during the process produce the stimula- 

 tion and modification of qualitative action which we recognize 

 as the specific medicinal or poisonous effect. 



Apparent Spontaneity of Vital Action. If life is thus merely 

 the action of a complex material compound, how are we to explain 

 the spontaneous movements and changes it apparently under- 

 goes 1 No matter how complex the protoplasmic molecule may 

 be, its atoms are still nothing but matter and must share its pro- 

 perties for good or evil, and among the rest, inertia. Hence it 

 cannot change its state of motion nor rest without the influence 

 of some force from without. True spontaneity of movement is, 

 therefore, just as impossible to it as to what we call dead matter. 



