THE BIOLOGICAL UNIT 29 



the cells of plants and animals, but the bitterest 

 denunciation was showered on the heads of those 

 who first stated that they were able to find cells in 

 the body of man, for this conclusion implied that 

 there was a scientific similarity between man and 

 animals. If the researches had revealed that 

 there was a different unit for man, then It is doubt- 

 ful if any common relationship could have been 

 established. 



If we are to understand man, the animal, we 

 must become familiar with the biological unit, as 

 the electrician Is with the watt or the chemist with 

 the atom. 



It was an English investigator In 1665 (Robert 

 Hooke) who first suggested the term cell to 

 describe the small cavities found in a thin section 

 of cork. The word as thus applied referred to 

 an empty space with a definite wall described as 

 "little boxes of cells distinct from one another," 

 but there Is no living substance In cork such as 

 Hooke examined. All that was present was the 

 empty shell. 



More than 150 years passed by before the scat- 

 tered observations of many students were core- 

 lated, and it was recognized that there Is a constant 

 structure In plants and animals. The long delay 

 In arriving at this simple generalization was large- 

 ly due ( I ) to the lack of appliances, such as the 

 microscope; and (2) to the fact that the attention 



