1890.] The Persistence of Plant and Animal Life. 519 
This is as true of a plant or animal as it is of a crystal, and 
until we learn what is the procedure in the act of growing mani- 
fested by plants and animals, we cannot assert that it is different 
from that in crystals. The framework of some living organisms 
is made up of minute crystals of carbonate of lime. It seems 
quite possible that the minutest component parts of either the 
cell or the perfectly visible crystal are crystalline, and that the 
next larger components, both in crystals and in organisms, are 
spheroidal bodies more or less resembling cells. : 
Another strong reason for believing that the smallest parts of 
organisms are crystalline in character, is the action upon them 
of polarized light. ? 
Without going more minutely into the explanation of these 
curious phenomena, it will be sufficient to say that bodies which 
are built up in such a manner as to exhibit greater density in 
one direction than another are said to be under the influence of 
polar forces of different degrees. Such building up is crystalline, 
and is apparent by the effect which the structure exerts on polar- 
ized light; and almost if not all organic solids show these effects. 
Dana continues: “ (3) It has the faculty of converting the nutri- 
ment received into the various chemical compounds essential to 
its constitution, and of continuing this process of assimilation as 
long as the functions of life continue; and it loses this chemical 
power when life ceases,” 
The crystal lives on what it can absorb from the liquids or 
semi-liquids, and from the gases surrounding it—probably never 
from the solids. In this it resembles the living thing. 
Moreover, it separates out of a solution containing many things 
the materials which it needs to continue the growth of itself, and 
rejects the rest, either pushing them aside or enclosing them as 
foreign bodies within its own structure. 
As to its losing this power when life ceases, the crystal’s life 
or growth may be said to last so long as there is a menstruum 
in which it can derive material for its further accretions, and to 
cease when this menstruum is withdrawn. But it can be resumed 
2 As pointed out by the speaker in a,lecture before the International Electrical Exhibi- 
tion in 1884. 

