LIFE: ITS NATUEE, ORIGIN AND MAINTENANCE 11 



between the colloidal solution constituting the protoplasm and the 

 circumambient medium in which it lives. Other similar films or 

 membranes occur in the interior of protoplasm. These films have in 

 many cases specific characters, both physical and chemical, thus favouring 

 the diffusion of special kinds of material into and out of the protoplasm 

 and from one part of the protoplasm to another. It is the changes pro- 

 duced under these physical conditions, associated with those caused by 

 active chemical agents formed within protoplasm and known as enzymes, 

 that effect assimilation and disassimilation. Quite similar changes can be 

 produced outside the body (in vitro) by the employment of methods of 

 a purely physical and chemical nature. It is true that we are not yet 

 familiar with all the intermediate stages of transformation of the materials 

 which are taken in by a living body into the materials which are given out 

 from it. But since the initial processes and the final results are the same 

 as they would be on the assumption that the changes are brought about 

 in conformity with the known laws of chemistry and physics, we may 

 fairly conclude that all changes in living substance are brought about by 

 ordinary chemical and physical forces. 



Should it be contended that growth and reproduction are properties 



possessed only by living bodies and constitute a test by which we may 



differentiate between life and non-life, between the 



Similarity of the am ' ma t e an( } inanimate creation, it must be replied 

 processes of growth . ' . 



and reproduction in that no contention can be more fallacious. Inorganic 

 living and non-living crystals grow and multiply and reproduce their like, 

 given a supply of the requisite pabulum. In rnost 

 cases for each kind of crystal there is, as with living organisms, a limit of 

 growth which is not exceeded, and further increase of the crystalline 

 matter results not in further increase in size but in multiplication of 

 similar crystals. Leduc has shown that the growth and division of 

 artificial colloids of an inorganic nature, when placed in an appropriate 

 medium, present singular resemblances to the phenomena of the growth 

 and division of living organisms. Even so complex a process as the 

 division of a cell-nucleus by karyokinesis as a preliminary to the multi-v , 

 plication of the cell by division a phenomenon which would primd facie 

 have seemed and has been commonly regarded as a distinctive mani- 

 festation of the life of the cell can be imitated with solutions of a simple 

 inorganic salt, such as chloride of sodium, containing a suspension of 

 carbon particles ; which arrange and rearrange themselves under the 

 influence of the movements of the electrolytes in a manner indistinguish- 

 able from that adopted by the particles of chromatin in a dividing nucleus. 

 And in the process of sexual reproduction, the researches of J. Loeb and 

 others upon the ova of the sea-urchin have proved that we can no longer 

 consider such an apparently vital phenomenon as the fertilisation of the 

 egg as being the result of living material brought to it by the sper- 

 matozoon, since it is possible to start the process of division of the ovum 



