Limits oF Divisitprinity oF Living MattTerR 3835 
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- 
aes 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 
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