THE WONDERS OF LIFE 



morphologically distinct nucleus, we should not yet have 

 shown its independence as an organellum of the cell. 



Nor is this any more proved from the circumstance 

 that in some bacteria (not all) we find a severance of the 

 plasm into an inner and outer layer, or a frothy structure 

 with vacuole-formation, or a special sharply outlined 

 membrane on the plastid. Many bacteria (but not all) 

 have such a membrane, like the nearly related chromacea, 

 and also the secretion of a gelatine envelope. Both 

 classes have also in common an exclusively monogenetic 

 reproduction. The bacteria multiply, like the chromacea, 

 by simple segmentation; as soon as the structureless 

 plasma-granule has reached a certain size by simple 

 growth, it is constricted and splits into two halves. In 

 the long-bodied bacteria (the rod-shaped bacilli) the 

 constriction always goes through the middle of the long 

 axis, and is, therefore, simple transverse cleavage. Many 

 bacteria have also been said to multiply by the forma- 

 tion of spores. But these so-called "spores" are really 

 permanent quiescent forms (without any multiplication 

 of individuals) ; the central part of the plastid (endo- 

 plasm) condenses, separates from the peripheral part 

 (exoplasm), and undergoes a chemical change which 

 makes it very indifferent to external influences (such as 

 a high temperature). 



The great majority of the bacteria differ so little mor- 

 phologically from the chromacea that we can only dis- 

 tinguish these two classes of monera by the difference in 

 their metabolism. The chromacea, as protophyta, are 

 plasmodomous. They form new plasm by synthesis and 

 reduction from simple inorganic compounds — water, 

 carbonic acid, ammonia, nitric acid, etc. But the 

 bacteria, as protozoa, are plasmophagous. They cannot, 

 as a rule, form new plasm, but have to take it from 

 other organisms (as parasites, saprophytes, etc.); they 

 decompose it by analysis and oxydation. Hence the 



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