BACTERIA AS PLANTS. 35 



VARIATION OF BACTERIA. 



This matter is made even more confusing by 

 the fact that any species of bacterium may show 

 more or less variation. At one time in the his- 

 tory of bacteriology, a period lasting for many 

 years, it was the prevalent opinion that there was 

 no constancy among bacteria, but that the same 

 species might assume almost any of the various 

 forms and shapes, and possess various properties. 

 Bacteria were regarded by some as stages in the 

 life history of higher plants. This question as 

 to whether bacteria remain constant in character 

 for any considerable length of time has ever been 

 a prominent one with bacteriologists, and even 

 to-day we hardly know what the final answer will 

 be. It has been demonstrated beyond perad- 

 venture that some species may change their 

 physiological characters. Disease bacteria, for 

 instance, under certain conditions lose their 

 powers of developing disease. Species which sour 

 milk, or others which turn gelatine green, may 

 lose their characters. Now, since it is upon just 

 such physiological characters as these that we 

 must depend in order to separate different species 

 of bacteria from each other, it will be seen that 

 great confusion and uncertainty will result in our 

 attempts to define species. Further, it has been 

 proved that there is sometimes more or less of a 

 metamorphosis in the life history of certain 

 species of bacteria. The same species may form 

 a short rod, or a long thread, or break up into 

 spherical spores, and thus either a short rod, or 

 a thread, or a spherical form may belong to the 

 same species. Other species may be motile at 

 one time and stationary at another, while at a 



