142 THE NEW PHYSIOLOGY. 



that we explain the movements of a limb. Similarly, 

 it is in terms of the interaction of oxygen molecules with 

 the molecules of haemoglobin and other substances in 

 blood that we explain the taking up of oxygen by venous 

 blood. The essence of the explanation or re-statement 

 of the event is that, after due investigation, we -have 

 assumed that the parts interacting in the event have 

 certain simple and definite properties, so that they always 

 react in the same way under the same conditions. For a 

 mechanical explanation the reacting parts must first 

 be given. Unless an arrangement of parts with definite 

 properties is given it is meaningless to speak of mechanical 

 explanation. 



To postulate the existence of a self-producing or self- 

 maintaining mechanism is thus to postulate something 

 to which no meaning can be attached. Meaningless 

 terms are sometimes used by physiologists ; but there 

 is none so absolutely meaningless as the expression 

 " mechanism of reproduction." Any mechanism there 

 may be in the parent organism is absent in the process 

 of reproduction, and must reconstitute itself at each 

 generation, since the parent organism is reproduced from 

 a mere tiny speck of its own body. There can be no 

 " mechanism " of reproduction. The idea of a mechan- 

 ism which is constantly maintaining or reproducing its 

 own structure is self-contradictory. A mechanism which 

 reproduced itself would be a mechanism without parts, 

 and therefore not a mechanism. 



Let us try to get nearer to what the self-reproduction 

 and self -maintenance of an organism implies. Perhaps 

 the clearest analogy in the inorganic world to the re- 

 production of an organism is the reproduction of a 



