ATROPHY AND DEGENERATIONS OF TISSUE. 55 



wall is in many cases non-evident, more particularly in embryonic 

 cells, in those of many rapidly growing new formations, blood 

 corpuscles, pus, and mucus ; that a cell is a small mass of matter 

 enclosimi a nucleus, and that the existence of a cell wall is due 

 to a degenerative process going on in the outer layers of the 

 mass. Thus Beale says, " A cell of epithelium consists of lio- 

 plasm or bioplasmatic matter, surrounded by formed non-living 

 matter, which was once in the hioplasmic state. In the same 

 way an oval yeast particle consists of the hiojylasm, with an 

 envelope of formed material, which has resulted from changes 

 occurring when particles upon the surface of the bioplasm died," 



Briicke, Strieker, and others consider that the existence of a 

 nucleus is not essential to the constitution of a cell ; and they base 

 their conclusions upon the fact that in some of the lowest forms 

 of life cells occur which show no trace of nuclei. Notwithstand- 

 ing this conclusion — that a cell is an elementary organism 

 capable of exhibiting all the phenomena of bfe — the nucleus is 

 exceedingly constant in all cells, and presents fewer varieties 

 in form and size than the cells themselves ; is spherical or oval 

 in shape, and often contains one or more minute round or angular 

 bodies — the nucleoli; offers greater resistance to chemical re- 

 agents than the other constituents of the cell, and in disease 

 often remains after these have been destroyed. It seems to be 

 structurally homogeneous or slightly granular, is more deeply 

 stained by carmine — a property peculiar to formative material 

 — and is in some cases invested by a limiting membrane. 



The cell contents have the power of spontaneous movement, 

 and these, as well as the alterations in form characteristic of 

 young cells, are due to the germinal living matter, which is pro- 

 bably the sole seat of the nutritive and formative power of the 

 cell. This germinal matter, or bioplasm, differs in volume and 

 consistence in different cells, and in the same cell at different 

 times. It is capable of imbibing and giving up fluids, and of 

 undergoing corresponding alterations in volume. 



It is now generally accepted that every cell originates from a 

 pre-existing cell, that tissue is formed by the natural formation 

 and growth of cells, and that the deviations from this process 

 constitute the basis of every pathological change. 



The multiplication of cells may take place — 1st. By simple 

 division ; 2d. By budding — gemmation ; and od. By the forma- 



