i] PROTOPLASM 7 



or artificial is usually not very serious in the majority of 

 bodies with which we shall have to deal; a comparison of 

 the results of various methods of fixation, and, when pos- 

 sible, of these with the living cell itself, is usually sufficient 

 to give at least a clear indication of the truth or falsity of 

 the representation seen in the stained preparation. But it 

 is important to remember that the preparations studied by 

 the cytologist are only representations or pictures of reality, 

 and not the reality itself; the real cell consists of viscid, or 

 at best semi-solid, substances suspended in a still more 

 fluid medium, while in the stained section these substances 

 are coagulated and rendered distinct by differential staining, 

 and it is hardly possible that this process can take place 

 without considerable deformation. Some portions of the 

 cell will be contracted and shrivelled, some swollen, and 

 some perhaps removed altogether, and careful comparison 

 of the results of different methods is needed before a true 

 idea can be obtained of the original form. 



Although the examination of the living cell gives good 

 ground for the belief that on the whole the methods used 

 by cytologists do in fact give authentic pictures of its real 

 structure, especially with regard to the nucleus and the 

 phenomena of nuclear division and also to the bodies em- 

 bedded in the cytoplasm, yet when these methods are 

 applied to the structure of protoplasm itself the doubt on 

 this point becomes a very real one. The reason for this is 

 that different methods of fixation give different appear- 

 ances, and the structure is so fine that it is practically im- 

 possible to check the results by comparison with the proto- 

 plasm of the living cell. There are four main hypotheses as 

 to the structure of protoplasm, three of which assume that 

 it consists of a more solid substance embedded in a more 

 fluid medium, while the fourth regards protoplasm as 



