52 
IOWA ACADEMY OF SCIENCES. 
which lies behind the entrance of matter. The energy of 
growth is but a special instance of osmotic pressure, the 
rhythms of which are expressive of the metabolisms in 
progress. 
The life-history of the metazoan cell involves many 
successive divisions, the earlier mitoses occurring rapidly, 
the later ones more and more slowly. There finally comes 
a time when the cell reaches its second critical stage, a 
condition of stability whose end is death. The first critical 
stage has been averted in the history of each organism 
through fertilization; but in the second critical stage, such 
a stimulus is clearly impossible for the metazoan cell. The 
w T ork of Calkins on Paramcecium, however, has demon- 
strated that an artificial substitute for conjugation may be 
found for the infusorian cell,— meat broth, extract of brain 
or pancreas,— w 7 hereby the second critical stage is passed. 
The bearing of this result on the metazoan cell is obvious. 
Probably certain tumors represent cells which, having 
approached the point of stability, have been stimulated to 
renewed activity by the presence of unusual ions. 
VII. CONCLUSION. 
Students of the animal cell may well look upon the re- 
sults of modern work with no small degree of satisfaction. 
A large body of solid knowledge concerning vital processes 
has grown up during recent years, very different from the 
vague and even mysterious assumptions w T hich lurked here 
but a short time ago. One conclusion to be drawn from 
the facts established is the marked degree to which 
physical principles have been extended into the domain of 
the vital. Some workers, as Le Dantec, swing the pendulum 
to the farthest limit in this direction, seeing nothing but 
mechanism in the life of a cell. Others there are, who, un- 
able fully to appreciate the physical basis of cell-life, insist 
on pushing the pendulum to the opposite extreme, calling 
this position vitalism; a position “where”, to quote Kant, 
“reason can repose on the pillow of obscure qualities.” 
The question properly may be asked, how rapidly is the 
investigation of the cell nearing its goal. Such an end is 
