THE LIVING MACHINE BUILDING FACTORS. 181 



doubtless, suggests to us that there may be simi- 

 lar forces at work in building protoplasm. If we 

 can find natural forces by which the simplest bit 

 of living matter can be built up into a complicated 

 machine like the ox, with its many delicately ad- 

 justed parts, it is certainly natural to imagine 

 that the same forces may have built this simpler 

 machine with which we started. But such a con- 

 clusion is for a simple reason impossible. We 

 have seen that the essential factor in this machine 

 building is reproduction, with the correlated 

 powers of variation and heredity. Without these 

 forces we could not have advanced in this ma- 

 chine building at all. But these properties are 

 themselves the result of the machinery of proto- 

 plasm. We have no reason for thinking that this 

 property of reproduction can occur in any other 

 object in nature except this protoplasmic machine. 

 Of course, then, if reproduction is the result of the 

 structure of protoplasm we can not use this factor 

 in explaining the origin of this protoplasm. The 

 powers of the completed machine can not be 

 brought forward to account for its origin. Thus 

 the one fundamental factor for machine building 

 is lacking, and if we are to explain nature's 

 method of producing protoplasm from simpler 

 structures, we must either suppose that the parts 

 of the cell are capable of reproduction and subject 

 to heredity, or we must look for some other method. 

 Such a road has however not yet been found, nor 

 have we any idea in what direction to look. 

 But the fact that nature has methods of machine 

 building, as we have seen, may hold out the pos- 

 sibility that some day we may discover her 

 method of building this primitive living machine, 

 the cell. 



