12 THE MAIN CURRENTS OF ZOOLOGY 



discovery of protoplasm came in 1835, though its 

 significance was not recognized until twenty-five 

 years later. This living substance, common to plants 

 and animals, had been casually observed, at inter- 

 vals, from 1755 onwards. Under the microscope its 

 movement had been detected in the proteus animal- 

 cule, by Roesel von Rosenhoff in 1755. Thereafter, 

 in plants, by Myen, in 1827, and by other observers. 

 But all these observations were substantially point- 

 ing out the existence of movements of a semi-trans- 

 parent jelly-like substance in animals and plants. 



An important forward step came in 1835 when 

 Felix Dujardin (1801-1860), a French naturalist, 

 published discriminating observations on this living 

 substance in simple animals such as various protozoa 

 and worms. Not content with merely observing its 

 movements, he experimented with it, and by applying 

 tests as to its solubility and behavior towards differ- 

 ent reagents, he distinguished between it and gum, 

 gelatine, mucus and white of egg, with which it has 

 superficial resemblances. Finally, in 1835, he de- 

 scribed it as a "living jelly endowed with all the 

 properties of life." His predecessors had not ob- 

 served it in this way; consequently, it is proper to 

 designate Dujardin as the scientific discoverer of 



