A child that is born in a =community of people= may become a railroad man and carry food and other freight from place to place; so, in the great =community of cells= (see Fig. 9) making up the human body, _the red blood cells, like the railroad man_, are employed in carrying material from place to place. But the community is old-fashioned, for the citizens build canals instead of railroads for their commerce (see Fig. 84). Just as a child may grow up to be a _farmer_ and aid in the conversion of crude soil into things suitable for the use of man, so _the digestive cells_ take the food we eat and change it into material with which the cells can build tissue. Some of the citizens of a community must, at times, take _the part of soldiers_ and policemen, and protect the community against the attacks of enemies. _The white blood cells_, already referred to, may be called the soldiers; for they go to any part attacked by injurious germs, a particle of poison, or other enemy, and try to destroy the enemies by devouring or digesting them. At other times they help to repair a break in the skin. If a splinter gets into the skin, the white blood cells form a white pus around the splinter and remove it. In fact, the white blood cell has been referred to as a kind of _Jack-at-all-trades_. In the human community there are certain persons who reach the positions of _teachers, lawmakers, and governors_; they instruct and direct the other members of the community. Just so, in the community of cells, there are certain cells called _nerve cells_ (see Fig. 11) that have the duty of governing and directing the other cells. The nerve cells are most abundant in the brain. Large cities must have _scavengers_. Likewise in the human body, a community composed of millions of cells, there are certain _cells in the skin and the kidneys_ which have this duty. They are continually removing impurities from the body.[4] [4] From Coleman’s “Hygienic Physiology,” The Macmillan Co., N.Y. [Illustration: FIG. 9.--VARIOUS CELLS of the body. (Jegi.) Tiny citizens of the bodily community.]