GROWTH 19 
the least how they increase in number; it is, however, 
something to have satisfied ourselves that they do so. 
To understand even a little of how it is done would 
demand a good deal of work, but, to put it as concisely 
as possible, each young cell increases in size until it 
is full-grown and then it divides into two by forming 
in its interior a new partition, and this sort of thing 
goes on over and over again in different parts of the 
plant’s body until it too is full-grown. That is how 
a plant grows, and that also is how we grow. 
Our body, like that of the plant, is built up of cells, 
and growth is brought about in each case by the 
repeated division of existing cells resulting in an 
increase not in their size but in their number. 
Now we must think of these three Factors of Life, 
Respiration, Nutrition, and Growth, as being very 
closely connected with one another. Respiration, the 
true function of which is to keep us warm and to 
supply us with energy to work and play, wears away the 
life-substance of our body, and nutrition repairs the 
waste by building it up again. They are the two truly 
vital functions upon which all life depends; but the 
third factor, growth, is not a vital function in the same 
sense, it is a result: it is the result of adequate nutri- 
tion. In healthy young children, animals, and plants 
nutrition adds more than respiration uses up, and so 
the body increases in size. In adults, on the other hand, 
respiration and nutrition are pretty evenly balanced, 
and so we keep the same size. If we are not properly 
nourished our body wastes visibly, and if we are gross 
and greedy in our feeding we are apt to become fat, 
coarse, and bad-tempered because we have taken more 
food than our body can use, and that is a very nasty 
and wrong thing to have done. 
