THE BACTERIA 15 



The Bacteria are the smallest known plants, and when 

 we consider the infinitesimal result of the activity of a 

 single individual, and yet grasp the enormous effects of 

 the activity of Bacteria in the aggregate, the pessimists 

 among us, given to minimizing the importance of the 

 human unit, may well take heart of grace. But while 

 these organisms teach us the value of the unit, we shall 

 have no desire to emulate them in the matter of multi- 

 plication. It is calculated that a single microbe, under 

 very favourable conditions, may have millions of de- 

 scendants in a few hours ! The bacterial population of 

 I cubic inch of cream standing about forty hours may 

 reach to 500,000,000 ! Most Bacteria love darkness 

 rather than light, and are killed by direct sunlight in a 

 few hours; they can stand diffused light much longer. 

 But some species of the Purple Bacteria — able to feed 

 on sulphide of hydrogen — thrive well in light, and are 

 attracted by it. 



Some authors consider Bacteria to form a distinct 

 group of Fungi ; they certainly display fungal characters ; 

 but perhaps it is premature to declare definitely that 

 they are Fungi, for we have yet much to learn about 

 them. They may be described as very minute one-cell 

 plants of the simplest structure, of a parasitic or sapro- 

 phytic nature, some of them capable of active move- 

 ments, and all, without exception, multiplying by trans- 

 verse division or fission ; they may also produce resting- 

 spores or -cells. They vary in form, and for convenience 

 in description are commonly classed as: — 



1. Spherical = Cocci (singular, coccus). 



2. Kod-like =Bacilli (singular, bacillus). 



3. Bent or Spiral Rods =Spirilla (singular, spirillum). 



4. Higher or Filamentous Bacteria =Tricliobacteria. 



