STUDIES OF SPORE-PLANTS 279 



the bacteria, and that the distance apparently covered must be 

 divided by the magnification of the microscope used in order to 

 learn the actual speed. Glass slides with delicate ruled lines have 

 been used to estimate the size and speed of the bacteria. Some of 

 those often seen are so small that 50,000 placed end to end would 

 make a row one inch long, and a bacterium rssinr of an inch long be- 

 longs to a giant species. 



In order to make bacteria more distinctly visible, it is customary 

 to stain them. A simple method is as follows. Place a drop of 

 fluid with bacteria on a cover- 

 glass, evaporate the water 

 slowly by holding the glass 

 above a gas-burner (a special 

 kind of forceps is made for 

 holding, but ordinary forceps 

 will serve), then pour over the 

 dry bacteria a few drops of FIG. 86. Forms of bacteria. 1, micro- 

 stain (gentian-violet, or other cocci . some in chains (streptococci), 

 aniline dyes dissolved in ? ******* ^ flagellated 3 bacilli 

 v . I. in chains. 4, spirilla. 5, bacilli with 



water). After twenty or more 8poreg ^ a dividing bacillus with 



minutes, wash off the stain by flagella. 

 dipping the slide into clean 



water, and then place the cover-glass on a drop of water on an object- 

 slide for microscopic examination. Be careful to get the stained side 

 of the cover-glass down. Instead of mounting with water, the cover- 

 glass may be carefully dried after washing off the stain, and mounted 

 with a drop of glycerin or Canada balsam. The glycerin will preserve 

 the preparation for several days, and the balsam makes a permanent 

 preparation which may be kept for years. 



Make brief examination of bacteria obtained from various sources, 

 such as sour milk, "mother-of-vinegar," and any organic materials 

 found in a state of decomposition. All bacteria seen will be spheri- 

 cal, rod-like, twisted, or spiral in shape, but they may be found 

 united together in groups. 



Bacteria may be found which show an enlargement due to the 

 formation of a spore (Fig. 86). These spores appear as dark spots 

 when the microscope is slightly out of focus, and very glistening 

 when in focus. " Hay-tea " made by pouring hot water over some 

 good hay, and filtering through a layer of cheesecloth, is excellent for 

 growing bacteria for study of spores. Fill several test-tubes half 

 full of "hay-tea, " plug with cotton, heat to 100 C. by holding tubes 

 in gas-flame until boiling occurs, or for a short time in a sterilizer. 



