Some Points in the Life-history of Bacteria. 125 



of oxygen. In Bacillus amylobacter, on the other hand, it is not 

 necessary to spore formation that the food material should be 

 exhausted. Moreover, some, at any rate, of the anaerobic 

 bacteria, i. e., bacteria which vegetate without free oxygen, 

 produce their spores anaerobically. The spores have a dense 

 sheath, which may be gelatinous in its outer part, and this con- 

 dition of the sheath enables the spores to resist agencies which 

 destroy the vegetative cells. They can resist a dry temperature 

 better than the same temperature in water. They can stand 

 ^J^ying. and are capable of sprouting after many months, 

 when placed in favourable conditions of warmth, moisture, and 

 nutrition. 



Colour. — Bacteria are mostly colourless, but there are excep- 

 tions. One, Bacterium chlonnum, contains chlorophyll, and is 

 said to decompose carbonic acid. Other bacteria appear coloured 

 red, orange, yellow, blue; while others, again, are colourless in 

 themselves but create colours in their nutrient media ; indeed, 

 it appears that even in bacteria-masses which show bright 

 colours, the pigment is in granules outside the cells, in fact that 

 the pigment in one case is soluble in water, in another is in- 

 soluble. The red colouring matter, however, called bacterio- 

 purpurin, found in one species, is allied to chlorophyll, and is 

 really contained within the cell. 



Distribution in Time and Space. — In time there is evidence 

 that a bacterium existed so far back as the Carboniferous Era, 

 for Van Tieghem has found in sections of silicified plants, which 

 were in process of softening at the time, remains of an organism 

 which exactly resembles Bacillus amylobacter of our day, and 

 appears to have had the identical function with it of destroying 

 the cellulose elements of plants. In space bacteria may be found 

 anywhere and everywhere. Yet that there is a difference in 

 specific distribution may go without saying, some species being 

 very common and others comparatively rare. I am not aware 

 that the experiment has been widely made, but I venture to pre- 

 dict that if in any part of the earth where vegetable and animal 

 life could be sustained, an ordinary infusion of organic matter 

 were exposed to the air for a longer or shorter time, the hay 

 bacillus and other common forms would make their appearance. 

 The reverse we know must obtain with regard to some of the 

 parasitic forms, as evidenced by cases where small-pox or 

 measles were introduced amongst a native community ile novo, 

 or reintroduced after long entire cessation. The North American 

 Indians, Greenlanders, and Icelanders, in the former case, and 

 the South Sea Islanders in the latter, were stricken down whole- 

 sale by the advance of the disease in a virgin soil. 



Habitat. — That many bacteria are strictly aquatic is well 

 known, and was shown in a very positive manner by Prof. Percy 



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