PRINCIPAL FUNCTIONS 
539 
and strong, it is the protoplasm that gives it that appear¬ 
ance. When a kitten runs and jumps, it is ‘the protoplasm 
of the cells that is active in reality. When a boy or girl 
skates or swims, we know that the good healthy protoplasm 
of the cells is at the bottom of such movements. So far as 
we can tell all protoplasm is much the same thing struc¬ 
turally and reacts in much the same way whether it is in the 
plant, kitten, or boy. 
When a plant grows, it is adding more cells; when the 
kitten grows, it is adding more cells; and the man is the boy 
with more cells added and more training and adaptation 
acquired. Nowhere in the animal or plant kingdom can we 
get away from the fact that the foundation of all organic 
structure is the cell. As each brick is a unit in a great 
building, so each cell is a unit in the huge tree by the road¬ 
side, the elephant in the zoo, or the great man leading his 
army. We are as old as our cells and the condition of the 
cells tells the story of health. Healthy cells make healthy 
bodies. 
Review the following : page 7; sections 6, 110; and figures 
4, 76, 195, 198. 
412. Principal Functions. — The principal functions of 
organisms are food-getting, digestion, assimilation, circula¬ 
tion, respiration, excretion, sensation, and reproduction. 
The food-getting methods of plants and animals vary widely. 
For the most part animals can move from a place of food 
shortage to another place where food is abundant. For the 
most part plants are anchored to a spot and must get their 
food there or starve. Animals take complex food sub¬ 
stances and break them down into simpler substances; 
while plants take simple substances and build them up into 
more complex substances. This is the great difference be¬ 
tween animals and plants as regards food-getting. 
The world is richer in food values because of the plants, 
whereas the animals tend to undo the work of plants. This 
