LIMITS OF DIVISIBILITY OF LIVING MATTER 335 



FIG. 93 



which, according to our experiments, is not far removed 

 from the limits of macroscopic visibility; I have empha- 

 sized the fact that for geometrical reasons alone a certain 

 amount of substance must be present before it is possible to 

 form a pluteus. But the lowest limit actually found is 

 reached very much earlier than that re- 

 quired from geometrical considerations 

 alone. Since it has been demonstrated 

 that the ultimate source' of all energy for 

 life-phenomena is of a chemical nature, 

 we must conclude from our experiments 

 that the ultimate unit of living matter 

 is such a quantity of substance as is 

 capable of developing that amount of 

 energy which is necessary for that life- 

 phenomenon which is used as a criterion. 

 In this we find a natural explanation of why the amount of 

 substance necessary for the formation of 

 a pluteus must be much larger than the 

 amount of substance which is sufficient 

 for the formation of a blastula, inasmuch 

 as a larger amount of living matter repre- 

 sents also a larger amount of energy. It 

 follows from this, also, that when one is 

 satisfied with spontaneity or irritability 

 as the criterion of living matter, the ulti- 

 mate unit of living matter is not only much 

 smaller quantitatively, but also different 

 qualitatively, as the protoplasm alone suf- 

 fices for this. In the case of ultimate units we not only deal 

 with masses which represent a definite amount of chemical 

 energy, but we have every reason for assuming that the 

 mode of liberation of this energy follows a definite order, 

 which is possibly the same for all life-processes. Our fur- 



FIG. 94 



