THE PHYSICAL BASIS OF LIFE 29 



jiersisteiit identity, perpetuating tliemselves by growth 

 and niultiplieation witliont loss of their specific individ- 

 ual type. These possil)ilities, long since urged l)y specu- 

 lative writers, have in recent vears been treated as almost 

 negligil)le; Imt sooner or later, I think, they will call for 

 more serious consideration, particulai'ly in view of the 

 results of eml)ryol()gical investigation, presently to be 

 considered. 



Among these possibilities the one least likely to meet 

 with approval is that some, and possible many, of the 

 sub-microscopical components may be self-perpetuating. 

 Good biological society long since placed its ban on medi- 

 aeval notions of this type and turned a cold shoulder upon 

 all corpuscular or micromeritic conceptions of the cell- 

 substance. Seriously to consider anything approaching to 

 them requires at this day a certain amount of courage. By 

 some singular process of casuistry such conceptions have 

 been supposed to place the fundamental problems of biol- 

 ogy beyond Hhe reach of scientific investigation. An in- 

 genious philosopher has said that corpuscular hytheses in 

 general would make of the world — or of the cell — a mere 

 puzzle-picture winch we cut up into small pieces only to 

 put them together again to form the same picture. In 

 spite of this, however, jDhysical science pursues its task of 

 cutting the w^orld up into smaller and smaller pieces and 

 has thus far seemed to manage fairly weW with the pic- 

 tures rebuilt from them. Similar in principle was the pro- 

 cedure of the fathers of the cell-theory when they resolved 

 the living body into its component cells. Some of the suc- 

 cessors of those pioneers, even doA\Ti to our o^\ai day, have 

 seemed to find something very reprehensible in this op- 

 eration : nevertheless the cell-theorv still seems to survive 

 as an effective means of biological progress. Perhaps 

 therefore the youthful sciences of cytology and genetics 



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