CELLS AND TISSUES 2/ 



composed. Before passing to the study of any of the in- 

 ternal organs, it will be necessary to study more thoroughly 

 the nature of cells. The unit of structure of animals and 

 of plants is a minute object called the cell, and each of their 

 tissues and organs is composed of many cells. The living 

 substance of which the cell is made is called protoplasm 1 

 and this name is applied to the cell substance of both 

 animals and plants. Workers with the microscope over 

 a century ago found that plant and animal tissues are 

 composed of little chambers, which they called cells. It 

 was found later that the liquid in the little chambers is of 

 more importance than the walls which the protoplasm 

 builds around itself. The wall was first called a cell; 

 now we use the word cell for the globule of living proto- 

 plasm together with its wall, if it has one. 



42. Protoplasm. We should not think because we use 

 the same name, protoplasm, for the substance forming the 

 cellular material of both animals and plants, that its 

 chemical composition is always exactly the same. This 

 varies in different cells, and is indeed so complex that 

 no chemist has ever been able to analyze it. The proba- 

 bility is that it will never be analyzed, as its complexity 

 seems unlimited. Besides, there is no such thing as dead 

 protoplasm. As soon as a chemist begins to analyze 

 protoplasm, it separates into a number of substances. It is 

 transparent and jelly like, yet under a microscope there 



many unreasonable and misleading notions. This is especially the case with 

 extremists, or with persons who entertain only one idea at a time. They are 

 unable to assign to each truth its proportionate importance. 



These are the persons who chill themselves in order to ventilate, worry 

 themselves about digestion, make themselves nervous while trying to develop 

 their muscles, etc. On the other hand, we all know of eases where a person 

 when young was the weakest member of the family; but who, through an intel- 

 ligent study of physiology and hygiene, became the soundest and healthiest 

 one in the family, and outlived those who were at first sound and strong. 

 1 Greek, protos, first; plasma, that which is molded. 



