Bacteria 



These living glows must not be confused with the 

 strange little flashing lights sometimes seen on the 

 tuberose in India, especially on very hot evenings. 

 This has not yet been explained, but seems to be due 

 to electric flashes. 



Spontaneous combustion, such as may happen to hay 

 and straw when stored in too wet a condition, is the 

 work of certain bacteria. On such damp grass stems 

 huge quantities of micro-organisms begin to grow and 

 are supplied by the organic matter diffusing out of the 

 hay. All these germs as well as any cells still alive in 

 the hay are actively breathing, taking in oxygen and 

 giving out carbonic acid. 6 Any heat produced is 

 retained, and the temperature gradually rises until the 

 whole stack bursts into flame. This is a special danger 

 on board ships laden with cargoes of cotton and other 

 vegetable matter. One of the bacilli lives at tempera- 

 tures of 50 to 6o° C, and its spores can resist a heat 

 of ioo° C. 



Besides light and heat, beautiful colours and strong 

 perfumes are often due to bacterial workings. Some 

 of these latter scents remind one of ripe strawberries ; 

 the " marigold " smell of African rivers described by 

 Mr. Kipling is also a bacterial bouquet. 



The colours are often quite vivid and beautiful. 

 There are several rich reds and pinks, of which the 

 crimson Micrococcus prodigiosus, with its extraordinary 

 resemblance to freshly shed blood, is the most interest- 

 ing. This is often to be seen on bread and other 

 provisions. Milk may become a deep blue, and there 

 are also light blues and purples and yellows ; a beauti- 

 ful fluorescent colour is formed by Bacillus lactis 

 aerogeneus. 7 Glue may be turned into a deep black 

 colour. 



Perhaps the prettiest of all is the rich golden russet 



60 



