208 THE AMEKICAN MONTHLY [September, 



pose the protoplasm of a set of cells, to select the power of metabolism 

 for special exercise, and in particular the power of producing starch, 

 and further that the cell store inside its own wall, the starch so formed 

 and hold it there, these cells would be recognizable as starch-producing 

 and storing tissue. Such a tissue forms the bulk of the potato tuber, a 

 valuable food for man, and another somewhat similar tissue is the liver 

 of animals, such as the sheep, dog, bird, fish, and others. Or the 

 chemical product formed by the cell's action, if the cells have special- 

 ized the metabolic power, may be a substance to be used in the con- 

 struction of a solid frame-work, which may be the cell-wall, thickened 

 as in the wood cells of plants, or a substance deposited in meshes be- 

 tween the cells as in the bone, or cartilage or tendon of animal bodies. 

 While the various similar cells of a tissue thus specialize one power, 

 and by their immense number make a total very vast in comparison 

 with their individual bulks, other sets of cells forming other tissues are 

 performing other collective activities, and securing equally important 

 results of other kinds. The example of another kind of tissue is fur- 

 nished by the ciliated cells lining the roof of the mouth of the frog, and 

 also the bronchial passages to the lungs. In this case we have hundreds 

 of cells forming ciliated tissue, each cell carrying hair-shaped prolonga- 

 tions, which specialize the fundamental power of motion ; the aggregate 

 work of these cells is a constant current outward from the lungs. 



Division of Labor — Organism Defined. — Tissues are the result 

 of a division of physiological labor whereby certain groups of cells in 

 a living body perform chiefly only one of the numerous powers of 

 protoplasm, and, having its chief energy directed in this one direction, 

 the other powers being exercised slightly or not at all, perform this 

 function better than it could if exercising all powers equally. The 

 principle of division of labor is well understood in man's social life. 

 Men can supposably perform all forms of work, both mental and physi- 

 cal with greater or less success, but the regular and constant perform- 

 ance of any one form improves the power of performing that form of 

 work. So cells can supposably do many things, but certain sets doing 

 regularl}' certain forms of physiological work become capable of doing 

 it better. Just as men have many needs when living together in a great 

 social organization, and certain sets work, to satisfy some needs, while 

 others, to fill other demands, so the tissues in a living body, being nu- 

 merous and variously located, perform a variety of functions all calcu- 

 lated to further the well-being of the sum of tissues. An organism 

 can now be defined ; it is a community of tissues, each tissue perform- 

 ing part in the life of the whole — giving and getting — affecting by its 

 health or disease the organism and affected by the health or disease of 

 the whole. The living body whether animal or plant is a microcosm, 

 the units are the cells. The only cases which are not included under 

 this statement are the unicellular animals or plants where no tissues 

 can be properly said to exist. 



Co-ordination. — Since the bodies of the higher plants and animals 

 are thus seen to be organisms composed of many different parts, and 

 since some ai-e very complicated by reason of the large number of parts, 

 it is easy to see that some systematic arrangement of the various labors 

 of the cells will be of advantage to the organism as a whole. And we 

 find that the tissues are combined in any bodies into organs for the per- 



