128 



ELEMENTS OF BIOLOGY. 



points, particles, or molecules (fig. 38, A). The largest of 

 these may not be more tlian one ten-thousandth of an inch 

 in diameter ; the smallest may not exceed one forty-thou- 

 sandth of an inch. Every increase in the magnifying 



* 



Fig. 38. A, Living particles or molecules developed in organic infusions. 

 B, Bacteria developed in organic infusions. (After Beale.) 



power of the microscope has simply served to bring to 

 light myriads of smaller and smaller particles ; and the 

 highest powers of the microscope known to us enormous 

 as they are only leave us in the certainty that if we could 

 obtain still higher powers, we should almost infallibly dis- 

 cover particles still more minute. All the particles of the 

 scum are seen to be in active and incessant movement, and 

 there is no question as to their being truly living organisms, 

 though it is uncertain whether they are of an animal or 

 vegetable nature, or whether they may not be partly the 

 one and partly the other. 



If the fluid be examined at a later period, in addition to 

 the minuter moving particles, there will be found many little 

 moving filaments of a larger size. Some of these are short 

 and staff-shaped, and are known as "bacteria" (fig. 38, B). 

 Others are long and worm-like, and move about actively, 

 twisting from side to side. These are known as " vibrios/' 

 Both the bacteria and vibrios are unquestionably alive, 

 though in this case, also, it is a matter of some doubt 

 whether we have to deal with animal or vegetable organ- 

 isms. Upon the whole, however, it seems tolerably certain 



