56 THE STORY OF THE LIVING MACHINE. 



But the fact is, when we turn our attention 

 in these two directions, we find the result is the 

 same. If we look for the lowest organisms we 

 find them among forms that are made of a single 

 cell, and if we analyze the tissues of higher animals 

 we find the ultimate parts to be cells. Thus, in 

 either direction, the study of the cell is forced 

 upon us. 



Before beginning the study of the cell it will 

 be well for us to try to get a clear notion of the 

 exact nature of the problems we are trying to 

 solve. We wish to explain the activities of life 

 phenomena in such a way as to make them intel- 

 ligible through the application of natural forces. 

 That these processes are fundamentally chemical 

 ones is evident enough. A chemical oxidation of 

 food lies at the basis of all vital activity, and it is 

 thus through the action of chemical forces that 

 the vital powers are furnished with their energy. 

 But the real problem is what it is in the living ma- 

 chine that controls these chemical processes. Fat 

 and starch may be oxidized in a chemist's test 

 tubes, and will there liberate energy ; but they do 

 not, under these conditions, manifest vital phe- 

 nomena. Proteid may be brought in contact with 

 oxygen without any oxidation occurring, and even 

 if it is oxidized no motion or assimilation or repro- 

 duction occurs under ordinary conditions. These 

 phenomena occur only when the oxidation takes 

 place in the living machine. Our problem is then to 

 determine, if possible, what it is in the living ma- 

 chine that regulates the oxidations and other 

 changes in such a way as to produce from them 

 vital activities. Why is it that the oxidation of 

 starch in the living machine gives rise to motion, 

 growth, and reproduction, while if the oxidation 



