BACTERIA 



To measure bacteria, we use the thousandth part of a millimeter, 

 called the micromillimeter, or micron, as the unit?* ^The Greek let- 

 ter fjt. is the symbol for this unit)AA micron is about Tskinr of an 

 inch, yet a bacterium one /* long, and a half /* in width, is very 

 large in comparison to some things that scientists measure, such 

 as the thickness of oil films, soap bubbles, or light-wave lengths, in 

 which the unit is a micro-micron, and is symbolized by /(//. The 

 shortest light-wave lengths are about 400 ///*, or .4 /i, while chromatic 

 threads in cells of bacteria are often 100 /*// in width. Then 

 again there are many things smaller than these threads. The thin- 

 nest part of a bursting soap bubble is but 7 /// 

 in thickness. There are certain infectious 

 agents that are submicroscopic; that is, in- 

 visible even by the aid of Siedentopf's 

 ultraviolet microscope, which shows objects 

 smaller by half a light-wave length (.2 fi/j). 

 ^ The structure of the bacterial cell is very 

 , 6. Diplococci simple. It consists of (i) a central nuclear 



showing capsules, body which can be stained like the nuclei of 



(Greene's Medical 



Diagnosis.) other vegetable and animal cells, with nuclear 



or basic stains, such as haematoxylin, or 

 methylene-blue. t 



< (2) A cytoplasm, or protoplasmic substance generally very thin. "4 

 *L(3) A cell wall, more or less thick, that stains with difficulty. 

 (Fig. 6.) 



'Lin the nucleus we often see metachromatic bodies, called the 

 Babes-Ernst granules, and unstained spaces called vacuoles, both of 

 which are common to many bacteria. These are both probably 

 due to ingested food or fluid. (* 



> Through the cell wall the food of the bacterium passes by osmosis. -)- 

 4** ihe cell wall of certain organisms, for example the pneumococcus, 

 undergoes a change whereby a mucilaginous or gelatinous capsule 

 is formed outside the cell wall. Its use is not known. The cell 

 wall is generally the first portion of the cell to be attacked by 



