40 THE STORY OF LIFE'S MECHANISM. 



sesses this power to induce the chemical change, 

 But apparently the process is of the simplest 

 character and involves no greater mystery than 

 chemical affinity. We know that the saliva con- 

 tains a certain material called a ferment, which is 

 the active agent in bringing about the change. 

 This ferment is not alive, nor does it need any 

 living environment for its action. It can be 

 separated from the saliva in the form of a dry 

 amorphous powder, and in this form can be 

 preserved almost indefinitely, retaining its power 

 to effect the change whenever put under proper 

 conditions. The change of starch into sugar is 

 thus a simple chemical change occurring under 

 the influence of chemical affinity under certain 

 conditions. One of the conditions is the presence 

 of this saliva ferment. If we cannot exactly 

 understand how the ferment produces this action, 

 neither do we exactly understand how a spark 

 causes a bit of gunpowder to explode. But we 

 cannot doubt that the latter is a purely natural 

 result of the relation of chemical and physical 

 forces, and there is no more reason for doubting 

 it in the former case. 



What is true of the digestion of starch by 

 saliva is equally true of the digestion of other 

 foods in the stomach and intestine. Each of the 

 digestive juices contains a ferment which brings 

 about a chemical change in the food. The 

 changes are always chemical changes, and are 

 the result of chemical forces. Apart from the 

 presence of these ferments there is really little 



chemistry. 



