82 REPORT — 1900. 



Great attention has been given to the structure of bacteria and to 

 their mode of propagation. When examined in the living state and 

 magnified about 2,000 times, a bacterium appears as a homogeneous par- 

 ticle, with a sharp definite outline, though a membranous envelope or 

 wall, distinct from the body of the bacterium, cannot at first be recog- 

 nised ; but when treated with reagents a membranous envelope appears, 

 the presence of which, without doubt, gives precision of form to the 

 bacterium. The substance within the membrane contains granules which 

 can be dyed with colouring agents. Owing to their extreme minuteness 

 it is difficult to pronounce an opinion on the nature of the chromatine 

 granules and the substance in which they lie. Some observers regard this 

 substance as nuclear material, invested by only a thin layer of protoplasm, 

 on which view a bacterium would be a nucleated cell. Others consider the 

 bacterium as formed of protoplasm containing granules capable of being 

 coloured, which are a part of the protoplasm itself, and not a nuclear sub- 

 stance. On the latter view, bacteria would consist of cell plasm enclosed 

 in a membrane and destitute of a nucleus. Whatever be the nature of 

 the granule-containing material, each bacterium is regarded as a cell, the 

 minutest and simplest living particle capable of an independent existence 

 that has yet been discovered. 



Bacteria cells, like cells generally, can reproduce their kind. They 

 multiply by simple fission, probably with an ingrowth of the cell wall, but 

 without the karyokinetic phenomena observed in nucleated cells. Each 

 cell gives rise to two daughter cells, which may for a time remain attached 

 to each other and form a cluster or a chain, or they may separate and 

 become independent isolated cells. The multiplication, under favourable 

 conditions of light, air, temperature, moisture, and food, goes on with 

 extraordinary rapidity, so that in a few hours many thousand new indi- 

 viduals may arise from a parent bacterium. 



Connected with the life-history of a bacterium cell is the formation in 

 its substance, in many species and under certain conditions, of a highly 

 refractile shiny particle called a spore. At first sight a spore seems as if 

 it were the nucleus of the bacterium cell, but it is not always present 

 when multiplication by cleavage is taking place, and when present it does 

 not appear to take part in the fission. On the other hand, a spore, from 

 the character of its envelope, possesses great power of resistance, so that 

 dried bacteria, when placed in conditions favourable to germination, can 

 through their spores germinate and resume an active existence. Spore 

 formation seems, therefore, to be a provision for continuing the life of the 

 bacterium under conditions which, if spores had not formed, would 

 have been the cause of its death. 



The time has gone by to search for the origin of living organisms by a 

 spontaneous aggregation of molecules in vegetable or other infusions, or 

 from a layer of formless primordial slime diffused over the bed of the ocean. 

 Living matter during our epoch has been, and continues to be, derived 



