1879. | Ultimate Physical Unit of Living Matter. 15 
The plastidule of Haeckel is hypothetically the molecule of 
protoplasm, and therefore the simplest possible form in which 
protoplasm can exist as protoplasm. The theoretically high 
degree of complexity of the molecule of protoplasm renders it in 
the highest degree susceptible to influences brought to bear upon 
it by its environment. Primarily its atomic constitution C H ON, 
must be related in some way to its properties. 
Haeckel attributes to every existing atom a modicum of force 
or energy as eternal and quantitatively unchangeable as the atom 
itself, which he calls the atom-soul; by aggregation of the atoms 
into chemical compounds, the mode and nature of the manifes- 
tation of individual atomic energies become mutually modified, 
and as resultants we have different properties and behavior mani- 
fested by such different compounds. By a long process of differ- 
entiation a compound was finally evolved answering in composi- 
tion and properties approximately, or entirely, to existing proto-. 
plasm. ‘his highly unstable matter, representing the aggregate 
or resultant of the energies of its component atoms as the energy 
of living matter, became the ancestor of some primordial amor- 
phous being out of which, by adaptation and “survival of the 
fittest” the ancestors of the Protista became differentiated. On 
the principle that motion or impulses once imparted to bodies 
tend to be perpetuated in the absence of other interfering causes, 
the energy of movement, called life, once set going tended to be 
kept up, and in order that it could withstand the interference of a 
great variety af disturbing causes, it gradually acquired the power 
of adaptation. This adaptation being simply vibration of. its 
molecules in unison with outer conditions as a resultant of those 
conditions. . From the well known postulates in regard to the 
persistence of matter and motion, it is clear that the molecules of 
different masses, subjected to differing conditions, would grad- 
ually acquire different modes of molecular motion, which would 
tend to be persistent and perhaps approximately alike throughout 
the same mass. Any part of this mass broken off would tend to ~ 
retain the molecular movements and consequently the properties 
of that of which it at first formed a part, but the new conditions __ 
to which it might become subject in the event of separation, ren- | 
der it probable that these motions might have others superadded, © 
or the old ones so changed as to give rise to different phenomena. 
Different food, tempered surrounding, media, etc., are thinkable __ 
