134 



THE MICROSCOPE. 



Sept. 



oped. There is, however, no differentiation in the bac- 

 teria into parts, such as root, stem and leaves, as in the 

 higher plants, or even as in the moulds where the portion 

 bearint^ the productive bodies is different from the grow- 

 ing part of the plant. So while not the lowest forms of 

 life, bacteria are perhaps the lowest forms with a definite 

 outline. 



Structure of Bacteria. — -Under a high power the in- 

 dividual bacteria are seen to be composed of a colorless, 

 homogenous substance known as })rotoplasn). The cell 

 wall is not always easy to see but is always [)resent and 

 by means of s})ecial reagents can be demonstrated. In 

 some cases it is flexible hut is usually (juite rigid and has 

 been found to consist not of a singb^ layer but of at least 



^ 



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two. The outer one may i)e more or less mucilaginous 

 in consistency; this often manifests itself as a capsule, 

 as in the case of the organism of crou})OUs pneumonia, 

 see Figure 2, No. 1; in otiier cases it is indicated by the 

 tendency of tlie individuals to unite or rather remain at- 

 tached to their fellows. 



The Size of Bacteria. — As regards size bacteria are 

 the smallest forms of life known. — The unit of measure 

 employed in microscopy is a micron or 1-1000 of a mm. 

 (about 1-25000 of an inch). Applying this measure we 

 find the dimensions of many of the forms do not exceed 

 a single unit. It is scarcely possible to realize their min- 

 uteness. If forms of this size were placed side by side 

 there would be 25,000 to a single linear inch; 625,000,- 



