14 PROTOPLASM AND THE CELL 



thousandth of an inch in diameter. In the human body 

 there are probably several hundred million cells. 



The discovery of cells, therefore, had to await the per- 

 fection of the microscope. In the Seventeenth Century 

 a Hollander named van Leuwenhoek had so far pro- 

 gressed in grinding lenses that it became possible to see 

 small objects. These lenses aroused a great deal of curi- 

 osity and were eagerly sought by scientific men. Among 

 them was Robert Hook, an Englishman. In 1667 he 

 happened to slice a piece of cork with his razor and ex- 

 amined it with a microscope, and discovered to his aston- 

 ishment that it contained a great many tiny cavities. 

 Because of their appearance — something like the cells 

 of a prison — he gave them the name cell. This term 

 we still use, although it is perfectly evident that it is a 

 misnomer. The important part of the cell is not what 

 Robert Hook saw, namely, the hard cell-wall, but the 

 living protoplasm inside the wall, which he did not see. 



The Discovery of Protoplasm. — It was more than 

 one hundred years after Hook's discovery of the cell be- 

 fore any observer saw and published an account of what 

 we now know to be the living substance. The first ac- 

 count which one can recognize as describing protoplasm 

 was written in 1755. A few years later, in 1773, an 

 Italian abbot named Corti observed in the common water 

 plant namerl Cham that the contents of the cell were, 

 under certain conditions, in motion. Although he pub- 

 lished an account of his observation it seems not to have 

 attracted any particular attention until 1807 when this 

 fact was again observed in the same plant by a German 

 investigator named Treviranus. Still this observation 

 flirl not suggest to anyone that the moving substance 

 was alive. At that time there were many theories to 

 account for the growth of organisms, all of which appear 

 to us to-day to be fanciful, but it is probably due to this 

 fact that Treviranus's observation did not suggest the 

 connection between motion and life. It was not until 



