THE POSITION OF CYTOLOGY IN BIOLOGICAL SCIENCE 3 



demonstrated b,y a number of students of minute anatomy during tlie 

 seventeenth and eighteenth centuries. The earliest published picture of 

 such structure appeared in 1665 in a book by Robert Hooke. In the 

 -works of this period the term cells meant two things: simply cavities 

 bounded by walls like cells in a honeycomb, or globules of numerous 

 unrelated kinds. For the most part they were looked upon as subor- 

 dinate components of tissues rather than imj^ortant individualized units. 

 Early in the nineteenth century, attention shifted to the "juice," or 

 "slime," which had often been observed in the cells. By the middle of 



Fig. 1. — Living cells as they appear when illuminated against a dark background. 

 a, cell from hair of squash plant. The cytoplasm forms a thin sheet against the cell wall, 

 a series of streaming strands through the cell sap, and a large mass about the nucleus. 

 {After M. Heidenhain.) b, chick-embryo cell growing on glass surface in tissue culture. 

 In the cytoplasm are fat globules and filamentous chondriosomes. (After T. S. P. Strange- 

 ways and R. G. Canti.) 



the century it had become evident that this unique fluid, or 'protoplasm 

 as it came to be called, was the substance actually manifesting the 

 phenomena of life, the thick walls observed in so many plant tissues 

 being a product of its activit3^ In 1831, Robert Brown had pointed out 

 the nucleus as a normal and characteristic constituent of cells. This 

 made it easier to describe the typical cell as a mass of cytoplasm enclosing 

 a nucleus, to distinguish it thus from other globules \\\i\\ which it had so 

 often been confused, and to regard it as an important unit of organization. 

 To this unit the more appropriate term protoplast has since been applied, 

 although cytology's ow^n name remains as a reminder of an earlier con- 

 ception of the cell (kytos = hollow place). 



