THE BIOLOGY OF THE CELL SURFACE 



Animal cells are ready-made. We do not devise them; 

 nor can we have them according to specifications which we 

 ourselves set up. If, as some do, we regard living cells as 

 machines, we appreciate that they are ready-made; we do 

 not make them as physicists make their apparatus to prove 

 a theory or test an hypothesis. Still less do we know them 

 and their variables. We do not use them to prove theories; 

 rather, either we elaborate theories from our observations 

 on them, or, having set up a theory, attempt to establish 

 it by experiment. In either case we seek to know the 

 "machine" and not by machine-making to devise hypothe- 

 sis or establish theory. 



A cell is never a tool. Nor is it an instrument on which 

 to whet one's physics and chemistry. Living matter Is 

 never an excuse and living phenomenon never an oppor- 

 tunity for the display of the investigator's physico-chemical 

 knowledge. If we use an apparatus in order to determine 

 oxidation in an inanimate system or devise a sensitive 

 instrument to measure light, the apparatus or the instru- 

 ment is a tool; but if one determines oxidation in a cell, 

 the oxidation-determination is the tool; if one measures 

 light produced by a cell, the measurement is the tool. In 

 neither case Is the cell a tool unless one frankly wants to 

 compare its sensitivity for oxidation or light production 

 with that of a man-made machine which of course is an 

 entirely different reason from that of investigating the 

 properties named as peculiarities of a living thing. The 

 physicist devises a tool with which to measure a given 

 change or to test an hypothesis; the biologist tries to mea- 

 sure changes in the cell — and the measurements are then 

 the tool by which he evaluates the properties of the cell or 

 tests his postulates of what these properties are. 



I think that we can agree that in the experimental study 

 of the egg's development the aim is the analysis of the 

 stages found in nature through which the egg passes to 



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