before there were any tailors, food was prepared before there were any 

 cooks, and so on. We summarize this idea by saying that "function precedes 

 structure." Protoplasm is able, then, to grow the special organs, as well as 

 to perform the various functions. 



In spite of the many kinds of organs that we find in the human body 

 and other complex species, the orgajusm always acts as a whole. The various 

 functions, however different they may appear, are all junctions of proto- 

 plasm. It is this unity of the organism that makes life both significant and 

 interesting; the more complex the organism, the more varied its parts, the 

 more wonderful is the total life in variety and interest. 



Of course the human body does not come from joining together millions 

 of cells that were once distinct. Like other organisms, it develops from a 

 single cell that divides into two cells, each of which again divides, and so 

 on until millions are formed. The many different kinds of cells and the 

 many different organs appear gradually by a process of differentiation, and 

 the different tissues and organs gradually take on specializations in their 

 functions. The organism has been a unity from the first. It is only because 

 we have taken the body apart in our studies that we must ask ourselves how 

 the parts are kept working together. It may be more helpful to ask. How 

 comes a bit of protoplasm to take on such complex forms and grow itself 

 into so many specialized organs ? 



The various organs or systems do work together because they are, so to 

 say, continuous with one another. They make up, essentially, a unit of 

 protoplasm, confronting the world in all directions as one, in spite of the 

 many specialized parts. All cells are connected through the blood, which 

 distributes nutrients and oxygen and which removes the products of metab- 

 olism. All the body cells are sensitive to the slightest changes in the 

 chemical state of the blood, and they all bring about changes in the blood. 

 Operating through the blood are the hormones, which are sensitive not 

 alone to the chemical state of the blood, but to more specialized stimulations 

 by way of the nerves. In turn they act upon the entire protoplasm — counter- 

 acting, compensating, reinforcing. 



Finally, the irritability of protoplasm manifests itself, in the more com- 

 plex animals, by the formation of the nervous system. This reaches all parts 

 of the body; and it is sensitive to changes inside, as well as to the changes 

 and disturbances in the environment. The nerves are connected not merely 

 with the muscles and the organs of special sensation (eye, ear, tongue, and 

 so on), but also with the blood-vessels and with the ductless glands. Be- 

 cause of their extreme sensitiveness and their quick response, they constitute 

 a very striking system of co-ordination, or unification, in the body. 



In the behavior of every plant and every animal we are impressed by the 

 fitness of the actions and of the chemical processes. Plant and animal action 



339 



