cytology: the study of the cell 131 



molecules of myriad kinds, some simple, some ranging up to the most com- 

 plex molecules known, each kind of molecule having its own chemical proper- 

 ties, the sum total of all these properties adding up, when the molecules 

 are organized in just the right way, to what we call life. The huge complexity 

 of protoplasm does not require great mass or bulk, for even the largest mole- 

 cules are minute in comparison with the size of the cell, and the space neces- 

 sary to accommodate the total organization of these molecules is easily pro- 

 vided by the average-sized cell. 



That there is plenty of space for a system as complicated as protoplasm 

 in the cell is shown by a comparison of the size of an average cell with that 

 of the various molecules which make up protoplasm. Protoplasm is com- 

 posed of a skeletal framework made up of protein molecules, to which mole- 

 cules of other kinds are attached, the whole suspended or dissolved in water. 

 One of the substances found in some abundance in the cell is sugar. As 

 Sponsler has pointed out, there is room in an average-sized cell for 64 trillion 

 molecules of glucose (grape sugar), each with a molecular weight of 180 

 (i.e., it is 180 times as heavy as a hydrogen atom). It would take a person, 

 counting at the rate of one a second, over 2 million years to count 64 trillion. 

 The protein molecules which form the structural framework of the proto- 

 plasm are much larger than glucose molecules, averaging about 36,000 

 molecular weight. A cell with a volume a millionth that of the average rain- 

 drop is large enough to accommodate over 60 billion such protein molecules 

 of average size (about 25 times as many as there are people on the face of 

 the earth). Some of the protein molecules in the cell, however, may have 

 molecular weights as high as 6 million. There would be room for as many 

 as 500 million molecules of this size in such a cell. It is evident, therefore, 

 that a cell could even be much smaller than a millionth the size of an average 

 raindrop and still be abundantly able to enclose an enormous number of 

 molecules of all sizes and sorts and to permit a molecular organization so 

 complex that its properties would total that of life itself. 



The cell has been known for a long time, but its nature, its organization, 

 and the ways in which it functions have only recently begun to be elucidated. 

 Back in 1665, Robert Hooke, an Englishman, constructed one of the first 

 "microscopes" and with it saw many things never before seen by the eyes of 

 man — among them, the box-like structure of cork. The compartments which 

 he found to compose the structure of cork he called "cells" — he thought 

 that they were empty compartments, as indeed in cork they were, since cork 

 cells die soon after they have been formed and hence lose their contents. 

 It was not until nearly 200 years after Hooke that it became evident that 

 living cells are not walls surrounding empty spaces, but are masses of mate- 

 rial surrounded by walls or membranes. The gradual revelation of the struc- 

 tural characteristics of this material, the discovery that it is endowed with 

 the power of movement and able to react and respond in various ways to 



