BACTERIA 



elaborate apparatus; considerable technical skill is 

 required to prepare the plants for examination — 

 many of them indeed can only be seen after they 

 have been stained and lastly, to trifle with the 

 disease-causing members of the family may lead to 

 dangerous if not fatal results. 



Having issued our warning let us see what we can 

 do in the way of microscopic investigation. The 

 easiest subject with which to make a start is the 

 Hay Bacillus, Bacillus Suhtilis, not because it is the 

 largest of the bacteria by any means, but because 

 it is very easily obtained. Each plant measures 

 about five thousandths of an inch in length, so we 

 shall require a high magnification to examine it. 

 Having obtained a small quantity of hay, we musi 

 boil it in water for about three-quarters of an houi 

 and then set it aside for some hours. In due course 

 the water will contain hundreds upon hundreds oi 

 bacteria or, speaking more correctly, of bacilli. Foi 

 our work, we shall require a special kind of micro- 

 scope slide; instead of the piece of plain glass w( 

 have been accustomed to use we must obtain ond 

 with a circular portion, hollowed out from thl 

 centre. Having done so, we take a clean jglass roc 

 and, with it, transfer a drop of the water, con 

 taining the bacilli, to the centre of a clean cover 

 slip. Invert the coverslip so that the drop is or 

 the lower surface and place it over the hollo\^ 

 portion of the slide, in such a manner that the droj 

 still remains suspended from the coverslip; this ii 

 known as the hanging-drop method and require' 



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