THE PRESENT POSITION OF CELL-THEORY. 115 



The next step is to transfer this generalisation, founded on 

 experience, into a new region, to the functions of cells. In 

 order to do this we should possess the same experiences 

 with regard to the functions of cells which we possess 

 with regard to the functions of composite organisms. But 

 these experiences are entirely wanting. We observe that 

 protoplasm exhibits functions, that it assimilates, that it is 

 irritable, that it is contractile, that it is reproductive, and so 

 forth ; but who has been able to demonstrate or even to 

 suggest with any plausibility that there are structures 

 specially devoted to assimilation, to contractility, to irrit- 

 ability, and to reproduction in protoplasm? It is evident 

 that the absence of any such experiences has been felt by 

 many observers, who have accordingly studied protoplasm 

 with a view to finding the required structures, and some 

 are inclined to say that the nucleus or perhaps the centro- 

 some is reproductive, the amylum and aleurone bodies are 

 assimilative and so forth. But there are protozoa endowed 

 with active functions which have no centralised nucleus ; 

 the presence of centrosomes has yet to be demonstrated in 

 protozoa in general, and there are forms in which, as 

 Biitschli well points out, the protoplasm is homogeneous, 

 e.g., in the pseudopodia Gromia dujardini} The reader 

 should refer to Biitschli's work for a discussion of the sub- 

 ject of hyaline protoplasm (loc. cit., p. 262). The fact that 

 it exists is of the highest importance, for it shows that there 

 is living substance exhibiting the usual vital phenomena of 

 assimilation, contractility, etc., which, nevertheless, defies 

 all attempts to recognise an organisation which in the light 

 of previous experience would seem adequate to the effects 

 produced, and it shows also that the centrosomes, the 

 amylum grains, and their analogues, and the whole category 

 of granules are secondary phenomena, which may be 



1 Not only are there no granules in homogeneous protoplasm, but the 

 alveolar structure of it is unrecognisable. It is easily shown, however, that 

 the homogeneous substance is produced from alveolar protoplasm and is 

 capable of reconversion into it. The physical explanation of the dis- 

 appearance of the alveolar structure is given by Biitschli on p. 264 of the 

 English translation of his work. 



