84 BACTERIA less. 



of a rod constricted in the middle. But it is only by using 

 the very highest powers of the microscope that its precise 

 form and structure can be satisfactorily made out. It is then 

 seen (Fig. 14) to consist of a little double spindle, staining 

 very deeply with aniline dyes. By the employment of very 

 high powers it has been shown that the protoplasm of the 

 cell contains a nucleus and is covered with a membrane of 

 extreme tenuity formed either of cellulose or of a proteid 

 material. According to Dallinger, at each end is attached 

 a flagellum about as long as the cell itself. 



Bacterium termo is much smaller that any organism we 

 have yet considered, so small in fact that, as it is always 

 easier to deal with whole numbers than with fractions, its 



lis mm. 



Fig. 14. — Bacterium termo ( x 4CXX)), showing the terminal flagella. 

 (After Dallinger.) 



size is best expressed by taking as a standard the one- 

 thousandth of a millimetre, called a microniillimetre and 

 expressed by the symbol /x. The entire length of the 

 organism under consideration is from 1*5 to 2 /t, i.e. about 

 the ^017 '^"^- ^'^ ^^ TT2 5 0<y inch. In other words, its entire 

 length is not more than one-fourth the diameter of a yeast- 

 cell or of a human blood-corpuscle. The diameter of the 

 flagellum has been estimated by Dallinger to be about \ fx. 

 or g^iyiVrsir i"ch, a smallness of which it is as difficult to form 

 any clear conception as of the distances of the fixed stars. 



Some slight notion of these almost infinitely small dimen- 

 sions may, however, be obtained in the following way. Fig. 

 14 shows a Bacterium termo magnified 4000 diameters, the 



