THE MECHANICS OF THE LIVING MACHINE 319 



least reached an intelligible understanding of the process. 

 The more complicated phases of reproduction are, of course, 

 not explained by this simple process, not even the division of 

 a cell which we have seen to be very complicated; but if we 

 can explain this strange phenomenon even in its simplest form, 

 we have done much toward explaining the functions of repro- 

 duction in accordance with the principle of chemical and phys- 

 ical forces. 



VITAL FORCE OR VITALITY 



With all of the explanation given, we cannot believe that 

 we have reached a solution of life. There is clearly something 

 lacking, for we still have to ask the question why it is that all 

 of these chemical and physical forces play together in such 

 harmony within the living organism. Nowhere in nature can 

 the physical forces automatically carry on such functions except 

 in living organisms. It is quite possible to compare the animal 

 body to a locomotive at rest. But a locomotive at rest, even 

 if its boilers are filled with steam under high pressure, ,will 

 never exhibit any activity without an engineer to control the 

 forces that are contained in the machine. The living organism 

 has no outside engineer. What is there in the living organism 

 that corresponds to the engineer starting and directing the 

 machinery? To this question we have no answer. Some bi- 

 ologists claim that there is no more need of an engineer for a 

 living organism than for a clock, these scientists assuming 

 that the complexity of the machine gives it automatic activity. 

 Others would believe that in a living being there is something 

 that is absent in other machines, to which they would give the 

 distinct name of vitality. There are certain functions of this 

 machine, like sensation, thought, etc., that do not seem to be 

 explainable by chemical and physical laws, and one class of 

 biologists would group these functions together under the 

 general term of vitality. Others would claim that vitality 

 has no real meaning, but is only a name given to a combination 

 of functions possessed by certain machines. The question 



