32 THE SMALLEST LIVING THINGS 



The nucleus is absolutely essential for cellular activity; with- 

 out it protoplasm soon becomes lifeless. This is readily demon- 

 strated by cutting into pieces any large single-celled animal, such 

 as an Amoeba* proteus or a Stentor, so that some of the frag- 

 ments are without a nucleus. Such pieces invariably die, while the 

 piece which has a nucleus lives. The sizes, forms, and number of 

 the nuclei in different cells vary widely. Some cells have no 

 definitely formed nuclei but have the essential nuclear substances 

 distributed throughout the cytoplasm. Such is the case in bacteria 

 and spirochaetes, where no definite nucleus with its nuclear mem- 

 brane and contained nuclear substance, called "chromatin," can 

 be found. Chromatoid granules are distributed throughout the 

 bodies of bacteria and spirochaetes and at times are segregated 

 in dense masses to form the spores of bacteria and the "coccoid 

 bodies" of spirochaetes. Thus these minute things do not have 

 the same type of organization as do cells of more complex organ- 

 isms, and in view of this fact, the English biologist, Dr. E. A. 

 Minchin, in An Introduction to the Study of Protozoa, refers to 

 them as organisms of a non-cellular grade. 



The Nature of Protoplasm* 



Physically, protoplasm is a glassy, sticky, fluid aggregate of 

 substances, each of colloid (jelly-like) nature. Chemically, it is 

 not a definite single substance but is a mixture of substances which 

 are not in solution nor do they form a true chemical union. Their 

 physical state is analogous to, but infinitely more complex than, 

 an emulsion of oil and water. Protoplasm is denser than water 

 and does not mix with it, but upon rupture of the surface mem- 

 branes of a cell may be readily disintegrated in water. 



Chemically, protoplasm is a combination of organic sub- 

 stances of complex nature — proteins, carbohydrates, and fats — 

 together with many inorganic substances, such as salts of various 

 kinds, water, and gases, such as carbon dioxide and oxygen. Of 

 these, water is the most abundant component and subserves many 

 important functions. It is essential for bringing about the break- 

 ing down of the compound salts into their constituent elements, 

 thus setting these elements free to enter into new chemical com- 



* See "The Coming and Evolution of Life," page 9, figure G, in this Series. 

 t See "The Coming and Evolution of Life," page 10, in this Series. 



