118 GENERAL PHYSIOLOGY 



such as salts and water ; the latter gives to living substance its 

 requisite liquid consistency. 



In its main outlines the above is the picture that the anatomical, 

 microscopic, physical, and chemical investigation of living substance 

 has afforded. 



II. Living and Lifeless Substance 



But the picture of living substance is still incomplete. In the 

 above pages there have been presented the details of its composi- 

 tion as knovs^n at present, but the most essential point is still 

 wanting. In what does the characteristic difference between 

 living and lifeless substance consist ? This question is weighty, for 

 it contains nothing less than the problem of all physiology — namely, 

 the problem of life, which since the earliest times has had an 

 irresistible fascination for inquiring minds. 



As has already been seen, the conception of life has not been 

 always the same. Since its origin among primitive peoples, it has 

 become changed in diverse ways. We will now inquire whether 

 it is possible to outline the conception scientifically by considering- 

 the differences between living and lifeless substance. 



Because of the sharp distinction between objects that never 

 have lived, such as stones, and those that have lived and died, or 

 corpses, this undertaking must be extended in two directions- 

 — first, to the differences between organisms and inorganic sub- 

 stances, and, secondly, to the differences between living and dead 

 organisms. 



A. ORGANISMS AND INORGANIC BODIES 



1. Structural Differences 



In comparing organisms with inorganic substances, the mistake 

 has been made of contrasting the organism with a crystal, instead 

 of with a substance that has a consistency, and, in general, physical 

 relations similar to those of living substance, i.e., with a semi- 

 liquid mass. Because of this mistaken comparison, a host of 

 differences have been set up, the incorrectness of which is evident- 



Thus, it has been said that inorganic bodies have forms con- 

 structed according to simple mathematical laws and possessing- 

 perfectly definite angles and edges, while organisms have bodily 

 shapes that cannot be represented mathematically. It is not 

 necessary to cite in refutation the "crystallised human folk" 

 which Mephistopheles claims to have seen in his years of travel ;- 

 the untenableness of this distinction becomes clear when it is 

 recalled that, in the first place, mathematically simple body-forms 

 do actually occur among organisms, as in the Eadiolaria, which are 



