THE LIVING MACHINE BUILDING FACTORS. 207 



similar 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 adjusted parts, it is certainly 

 natural to imagine that the same forces may have 

 built this simpler machine with which we started. 

 But such a conclusion is for a simple reason im- 

 possible. 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 machine building at all. But these pro- 

 perties are themselves the result of the machinery 

 of protoplasm. We have no reason for thinking 

 that this property of reproduction can occur in 

 any other object in nature except this proto- 

 plasmic machine. Of course, then, if reproduc- 

 tion is the result of the structure of protoplasm 

 we cannot use this factor in explaining the origin 

 of this protoplasm. The powers of the completed 

 machine cannot 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 repro- 

 duction and subject to heredity, or we must look 

 for some other method. Such a road has how- 

 ever 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 possibility 

 that some day we may discover her method 



