32 BIOLOGY: GENERAL AND MEDICAL 



dissimilar to that of the growth of crystals, for example, 

 where it takes place by accretion, or the addition of 

 new matter to the surface, for it pervades the entire 

 molecular structure of the protoplasm by the actual 

 jj^MTv - ; interposition of the new molecules between those already 

 existing. When the function of synthesis keeps pace 

 with that of analysis, growth ceases, and when analysis 

 is more rapid than synthesis, life soon becomes extinct 

 and the protoplasm breaks up into simpler and simpler 

 compounds. 



3. Its tendency to undergo cyclical changes. 



The cyclical changes are largely incidental to the 

 phenomena of reintegration. Coming into being through 

 the activity of antecedent living substance, the living 

 organism proceeds to increase its own substance, to 

 dispose of that which is formed in excess of its own 

 needs by detaching it in the form of new individuals, 

 and finally when no longer able to maintain the equi- 

 librium of reintegration to disintegration, ceasing to live 

 and undergoing dissolution by destructive analysis, 

 but being survived by descendants behaving in the same 

 manner. 



The successful application of these criteria for the 

 recognition of life presuppose some acquaintance with 

 the supposed living substance. One cannot immediately 

 employ them for the determination of the living or not 

 living character of any particular object picked up 

 haphazard during a ramble through the country, for, 

 should the objects in question be inactive forms of life, 

 such as the seeds of plants, not only would confusion 

 arise from the evident dissimilarity of chemical composi- 

 tion occasioned by the presence of the starch, cellulose, 

 and wooden materials forming the most conspicuous 

 structures of the seed, but one would be at a total loss 

 in an attempt to immediately accord to the seed any 

 molecular activity or cyclical changes. A superficial 

 acquaintance with seeds is, however, sufficient to enable 

 the investigator to apply the second and third criteria 



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