2270 Journal of Applied Microscopy 



The amount of the centrifugal force may be calculated from the following 

 formula : 



4 ;r R (in meters) 4 tt^ . ^o < . . 

 ^ ^, = 4.024, a constant. 



gt- g 



R 



4.024 X — = no. of g (gravity), 

 t^ 



R = radius expressed in meters. 



t = time in seconds of one revolution. 



If the centrifugal force is greater than five times gravity it is better to use a 

 modification of the above apparatus, which I have described in a previous note^ 

 in this Journal, otherwise the intense force will either break the seedling or 

 tear it from its support. 



As stated in that note, it is better to insert the seedlings in short pieces of 

 glass tubing and pack them loosely with cotton batting, merely allowing about 

 five millimeters of the root tip to protrude. The pieces of tubing may be at- 

 tached to the bar with rubber bands. A supply of moisture may be introduced 

 by means of an atomizer. Howard S. Reed. 



University of Michigan. 



Bacteriology for High Schools. 



Copyrighted. 

 II. 



General Co/isiderations. The bacteria are so different from any object with 

 which we are familiar, both in size and appearance, and the methods of study so 

 entirely new that some brief general considerations seem necessary before we 

 begin their actual study. 



Nature of Bacteria. The bacteria have their nearest allies among the plants 

 and are, therefore, to be considered as plants rather than animals. 



Size. Bacteria are among the smallest of living things. In fact, they are so 

 small that it is very difficult to get even an idea of their actual size. The unit 



Fig. 8. — Form types of Bacteria. 



of measurement for microscopical objects is a micron (about one twenty-five 

 thousandth part of an inch). If this unit is applied to the bacteria we find that 

 ordinarily their shortest diameter is about one micron. This means that nearly 

 200 ordinary sized bacteria must be placed side by side to cover a space equal 

 to the thickness of the paper on which this is printed. 



Form. In form the bacteria are very simple. Briefly, all bacteria may be re- 



1 Journal of Applied Microscopy, Vol. IV., p. 1499- 



