SIZE. 



19 



to being organs of locomotion, aid to increase the food-supply 

 of the germ by stimulating the flow of the current of the 

 nutrient fluids past the bacterium. 



The so-called Brownian movement is observed frequently in 

 bacteria, and especially in the cocci. It is simply a molecular 

 movement or rearrangement of the protoplasmic granules 

 without changing the position of the organism in the least. 

 The spirilla frequently exhibit ajrotqry movement, which may 

 be very rapid. The movement due to the currents present in 



FIG. 1. 



a. Spiral forms with a flagellum at only one end. b. Bacillus of typhoid fever 

 with flagella given off from all sides, c. Large spirals from stagnant water with 

 wisps of flagella at their ends (Spirillum undula). (Abbott.) 



all fluids must not be confused with actual motility. Fre- 

 quently it is mistaken for such, especially when the organism 

 is examined in the hanging drop. 



Size : Bacteria vary greatly in size. The micromillimeter 

 is the standard of bacteriologic measurement. It is equal to 

 about 25ooo f an m ch. The cocci are the smallest bacteria, 

 and the twisted, spiral, or chain organisms the largest. The 

 cocci vary in size from O.I// to 2.8 ^e; the bacilli range from 

 1 p. X 0.2 p. to 5 1*. X 1 .5 fi.. The anthrax bacillus is the largest 

 of the bacillus group, and the bacillus of mouse septica3mia 

 the smallest. Some of the spirilla are as many as 40 fj. in 

 length (spirillum of relapsing fever). It is almost impossible 

 to form any definite conception of the size of bacteria. In 

 order to determine their measurements special microscopic 

 attachments are necessary. The weight can be arrived at by 

 a lengthy mathematical calculation. Naegeli estimated the 

 weight of an average organism at loooooooFOT of a milligram- 



