OSMOSIS 
15 
adding ever greater amounts of fats to their diet, until we 
come to the Esquimaux, who eat large quantities of pure fat 
with relish. Large amounts of fat are necessary to keep 
the body warm in the very cold zones. 
Mineral Foods. — Salt is a most important mineral food. 
It is so frequently used to give a flavor to our food that we do 
not realize its real importance. A well-nourished animal or 
plant must have it to a certain amount. Deer travel long 
distances for it. Most of the other minerals are found in 
ordinary food so that it is not necessary to use them as we 
do salt. 
Osmosis. — Foods in the form of solutions must be taken 
into the walls of the stomach and intestines and through the 
cell walls of plants. These structures have no pores that 
we are able to see with a microscope and yet the solutions 
pass through. This passing of food and water through animal 
and plant cells is osmosis. The term osmosis is also used 
when a gas, such as oxygen, passes through the skin or lungs 
into the blood. From time to time further explanations of 
this very complex process will be made. A simple device 
for illustrating osmosis is described in Science , Dec. 12, 1919, 
page 542, by Elbert C. Cole. 
