THE GENERAL CONDITIONS OF LIFE 



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the fulfilment of all external conditions is the presence of a 

 substance, capable of life, in which vital phenomena can take 

 place. Hence, if a tiny drop of living substance be imagined in a 

 medium in which all the external conditions of life are fulfilled, it 

 must be assumed that it will remain living so long as disturbing 

 influences do not enter from without. But experiments 

 contradict this. 



A small mass of living substance can be easily obtained by 

 cutting off with a fine scalpel under the microscope a piece of 

 hyaline protoplasm from a living cell, e.g., Amoeba. The piece cut 

 off is living ; this is recognised from the fact that after the opera- 





PIG. 133. Stentor roeselii, a ciliate-infusorian cell. The clear, extended, rod-shaped mass in the 

 interior is the nucleus. A, Cut into two nucleated pieces at * ; at B and Cthe nucleated pieces 

 have become regenerated into whole Stentors and continue to live. 



tion it still performs such movements as the whole Amoeba 

 performs. The external vital conditions, moreover, are all 

 fulfilled, for the part exists in the same medium and has the same 

 external relations as the whole Amasba. Nevertheless, it lasts for 

 a short time only, it soon dies and cannot be restored to life by 

 any agency. Every like experiment without exception upon any 

 other cell yields the same result (Fig. 133). In all such cases 

 a certain mass of living substance exists in a medium in which all 

 external vital conditions are fulfilled, and yet the mass cannot 

 continue living. Hence some factor among the general conditions 

 of life is wanting. 



