274 
R. A. HARPER 
The cell theory that higher organisms are complexes of simpler organisms 
which by their manifold interactions build a more differentiated organic 
unit was never more firmly established, more thoroughly in harmony with 
all known facts, than it is to-day. Opponents there are of this doctrine, 
but even they admit that the great problem to be solved is the discovery of 
the organization of protoplasm, and this search to discover the real structure 
of the protoplasm is the goal of all cell studies. There is no real diversity 
of opinion between biologists as to the significance, the methods, and the 
goal of cytological investigation. The viewpoint which I wish to emphasize 
is that the structure of protoplasm is the structure of the cell. The search 
for some ultra-microscopic structure of living substance as such and more 
deep-seated than cell structure, has, so far, proved as vain as the older 
attempts to demonstrate the existence of a vital force. 
To the theoretical biologist the biological sciences, old and new, anatomy, 
surgery, physiology, pharmacology, pathology, bacteriology, and genetics — 
these great fields of human thought and effort which have borne fruits of 
such inestimable value for civilization and the progress of the human 
race are all of interest as they contribute to the explanation of the cell 
structure and its functions, for to-day no really critical student of biology 
questions that in the organization of the cell lies the world-old riddle as to 
the nature of life, its origin, possibilities, and limitations. 
The cell theory with its varied implications lies at the center of all 
biological thought and interest, and the history of the cell theory has been a 
continual vindication of the methods of observation and analysis as against 
the loose and easy methods of a priori speculation. No philosopher ever 
guessed that life units as we know them arise only by division, that the 
fertilization of the egg is the fusion of cells, or that heredity is based on a 
painstakingly equal division of a germ plasm. Whatever we may believe 
about pre-established harmonies in the organization of the universe, it is 
obvious that our minds are not so constituted that it is easy for us to guess 
the truth or that whatever is true about the cell seems natural and to be 
expected. The great discoveries of biology have been reached by the 
laborious and sometimes seemingly almost blind method of trial and error, 
with error always largely in evidence. 
We are inclined to speak of the present as a period of criticism and of 
the application of fundamental discoveries of science to practical affairs, 
but it seems to me equally obvious that, as noted, the new data in chemistry 
as well as from experimental breeding and cytology are gradually and some- 
times perhaps almost subconsciously changing our viewpoints as to many of 
the old conceptions of life and protoplasm. We can perhaps, as I have 
suggested above, classify in three groups the movements and discoveries 
which are influencing our conceptions of life structures and life processes. 
I shall speak of the contributions of cytology, of the chemistry of the colloids, 
and of genetics to our conceptions of protoplasm. 
