Chap, i.] THE CELL. 7 



whom it must be explained ; it was, however, first 

 observed by an eminent botanist, and is consequently 

 known as the Browiiian movement. 



The term cell is not unfrequently applied to 

 every separate mass of living matter, but, in conse- 

 quence of the associations connected with this term, 

 it is better to make use of the more elaborate though 

 perhaps more intelligible nomenclature which enables 

 us to distinguish between the different characters of 

 "elementary organisms." When attention was first 

 directed to these objects, the botanist observed that in 

 each mass of protoplasm there was a portion which, 

 by various characters, could be easily distinguished 

 from the rest, and which might be very appropriately 

 spoken of as the nucleus ; in addition to this, he 

 saw that the outer portion of the protoplasm was en- 

 closed as in a wall ; he spoke, therefore, of the whole 

 as a cell, with a cell wall, and a contained nucleus. 



Later on it was found that the protoplasm (or 

 " sarcode," as it was originally called) of animals was 

 not to be distinguished from that of plants, and it 

 was then also seen that it was only in very rare cases 

 that this animal protoplasm was enclosed in a cell 

 wall. Thereby the very first conception of a cell was 

 destroyed, but the name was still retained as a con- 

 venient term. 



Still later researches revealed the at first 

 astonishing fact that organisms could and did exist 

 in which that specially modified portion of the proto- 

 plasm which had been called the " nucleus " was, to 

 all appearance, altogether absent ; some naturalists, 

 and especially some physiologists, now regard the 

 nucleus as no essential part of the cell. On the other 

 hand, it seems better to recognise in our nomenclature 

 the present conditions of our knowledge, and to use 

 for the " elementary organism " some other definite 

 term than that around which so many battles have 



