22S 



molecule having its own chemical 

 properties, the sum total of all these 

 properties adding up, when the mole- 

 cules are organized in just the right 

 way, to what we call life. 



Tliat there is plenty of space for a 

 sj'stem 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 hy- 

 drogen atom). The protein molecules, 

 which form the structural framework 

 of the protoplasm are much larger than 

 glucose molecules, averaging about 36,- 

 000 molecular weight. A cell with a 

 volume a millionth that of the average 

 raindrop is large enough to accommo- 

 date over 60 billion such protein mole- 

 cules 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 

 milhon. There would be room for as 

 many as 500 million molecules of this 

 size in such a cell. It is evident, there- 

 fore, that a cell could even be much 

 smaller than a millionth the size of an 

 average raindrop and still be abun- 

 dantly able to enclose an enormous 

 number of molecules of all sizes and 

 sorts, and to permit a molecular or- 

 ganization so complex that its prop- 

 erties 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. 



CYTOLOGY 



Back in 1665, Robert Hooke, an Eng- 

 lishman, constructed one of the first 

 "microscopes," and with it saw many 

 things never before seen bv the eyes of 

 man— among them, the box-like struc- 

 ture of cork. The compartments which 

 he found to compose the structure of 

 cork he called "cells"— he thought that 

 they were empty compartments, as in- 

 deed, 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 material surrounded 

 by walls or membranes. The 1870's 

 and 1880's were especially significant 

 in the history of cytology. It was during 

 this period that chromosomes were dis- 

 covered, that the details of cell division 

 were worked out, that the foundations 

 for the study of the structure, chemical 

 composition and behavior of proto- 

 plasm were laid. 



If one were to ask why it took so 

 long after the cell was first seen for 

 the science of cytology to be bom, the | 

 answer is easy. Cytology, dealing as it ' 

 does with units of microscopic size, 

 had to await the development of mag- 

 nifying apparatus of sufficient strength 

 and resolving power to enable objects 

 as small as a cell to be studied in de- 

 tail. Such instruments were not de- 

 veloped until the latter third of the 

 19th century. | 



Ever since its birth, cytology has 

 been limited in its achievements by the 

 instruments and methods at its dis- 

 posal. On the observational side, it has 

 been limited by the ability of available 

 equipment to magnify and resolve. The 

 microscope which uses ordinary light 

 can only magnify in a really satisfac- 

 tory manner up to about 2500 diam- 

 eters, and this result has only been 

 achieved by the use of special tyqpcs of 

 optical materials, such as fluorite. At 

 higher magnifications, the image be- 



