xvi] ORIGIN OF LIFE 263 



it may be that a combination of comparative and experi- 

 mental cytology will lead to a truer conception. In this 

 connection reference must be made to MINCHIN'S Presiden- 

 tial Address to Section D of the British Association in 1915, 

 written very shortly before his death. It is impossible in a 

 short space to give an adequate account of this most sugges- 

 tive and illuminating paper, but its central idea may be 

 shortly summarised. MINCHIN points to the facts that the 

 nucleus, or, in some Protozoa, the chromatin granules 

 (chromidia) which represent it, is essential to the life of the 

 cell ; that in the nucleus the chromosomes or other chroma- 

 tin particles seem to be the essential portion ; and that the 

 chromatin particles are the only constituents of the cell that 

 are not only universally present, but also seem to have a 

 continuous existence and individuality through all cell- 

 generations. These facts suggest that the most primitive 

 living organisms were composed, not of a homogeneous sub- 

 stance resembling cytoplasm, but of chromatin or something 

 nearly allied to it. They were possibly very minute, even 

 ultramicroscopic, and their nearest living relatives may be 

 the ultramicroscopic and unfilterable organisms that are 

 responsible for such diseases as Measles and Yellow Fever. 

 From these primitive chromatinic corpuscles ("biococci") 

 MINCHIN imagines that evolution may have proceeded on 

 two lines. On the one hand they may have developed an 

 enveloping membrane and have given origin to the Cocci 

 and Bacilli known collectively as Bacteria. On the other 

 hand they may have evolved an outer viscous or semi-fluid 

 layer of "periplasm," and from being holophytic in habit 

 have taken to ingesting solid food by means of this amoeboid 

 covering, within which the biococci could multiply and form 

 a group of chromatin granules enclosed in a mass of primi- 

 tive cytoplasm. From such a condition it is not difficult 



