278 LIFE AND DEATH. 



at once. They are produced rapidly for one part, and 

 more slowly for a small remaining portion. Bars of 

 ferro-nickel which have been kept at the same 

 temperature change gradually in length in the course 

 of a year. Can we find a better proof of internal 

 activity occurring in a substance differing so greatly 

 from living matter? 



Nature of the Activity of Particles. — These are 

 examples of the internal activity that occurs in brute 

 bodies. Besides, these facts that we are quoting 

 merely to refute Bichat's assertion relative to the 

 immutability of brute bodies, and to show us their 

 activity, also afford us another proof. They show 

 that this activity, like that of animals, wards off 

 foreign intervention, and that this parrying of the 

 attack, again like that of animals, is adapted for the 

 defence and preservation of the brute mass. So that 

 if we consider of special importance the adaptative, 

 teleological characteristic of vital phenomena, a 

 characteristic which is so easily made too much of 

 in biological interpretations, we may also find it 

 again in the inanimate world. To this end we may 

 add to the preceding examples one more which is 

 no less remarkable. This is the famous case of 

 Becquerel's process for colour-photography. 



Colour- Photography. — A greyish plate, treated with 

 chloride or iodide of silver and exposed to a red light, 

 rapidly becomes red. It is then exposed to green 

 light, and after passing through dull and obscure 

 tints it becomes green. To explain this remarkable 

 phenomenon, we cannot improve on the following 

 statement :— The silver salt protects itself against 

 the light that threatens its existence ; that light 

 causes it to pass through all kinds of stages of 



