44 
IOWA ACADEMY OF SCIENCES. 
III. THE NUTRITION OF THE CELL. 
The ingestion of matter, standing as the alpha of cell- 
life, may well command attention. It is somewhat unfor- 
tunate that laboratory studies of the Protozoa exhibit so 
prominently the entrance of solid matter into the cell, for 
this condition is really quite rare in the animal series. 
Matter is so universally floated into the cell in water that 
the problem of its entrance is, in fact, the problem of the 
absorption of a solution. The field is a promising one for 
further research, but sufficient has already been done to 
show that the principles of osmotic pressure find applica- 
tion here. The architecture of protoplasm and its chem- 
istry are such that conditions for a greater or less amount 
of osmotic pressure are always present. Now, since food 
reaches the cell in solution, van’t Hoff’s work on osmotic 
pressure shows that its absorption is not a peculiarly mys- 
terious phenomenon, but that the vital results are in har- 
mony with the principle of the conservation of energy. 
Even the choice of matter, so universally exercised by the 
cell, rests on relative osmotic pressures, depending upon 
the peculiar constitution and chemical reactions of the 
protoplasm in each instance. 
The transforming effects upon matter of enzymes hold 
so necessary a place in animal life that attention has long 
been directed to this field. Here again, the understanding 
of the principle involved places the biologist in the debt of 
the physical chemist. The study of colloidal solutions or 
sols of metals has been illuminating to a remarkable de- 
gree. Platinum, gold, silver, iridium, — when brought to 
an extremely minute state of subdivision, by methods 
which need not here be described, behave as catalyzers to 
such an extent that these sols have been called “inorganic 
models of the enzymes.” An enzyme is, of course, immen- 
sely complex in composition as compared with the inor- 
ganic model, being the result of cellular activity — a nucleo- 
proteid; but its minute subdivision is certainly at least as 
important as its chemistry. 
