28 ELEMENTARY BIOLOGY. [iV. 



h. Bacillus. Threads composed of straight cylindri- 

 cal joints much longer than those of Bacteria, but 

 of a similar structure: they are always free- 

 swimming. 



c. Vibrio. Like Bacillus, but with bent joints. 



d. Spirillum. Elongated unjointed threads rolled 

 up into a more or less perfect spiral : frequently 

 two spirals intertwine. In some of the largest 

 forms a vibratile cilium can be made out on each 

 end of the thread. 



e. Spirochete. Much like spirillum, but longer and 

 with a much more closely rolled spiral. A very 

 actively motile but not common form. 



7. Examine various putrefying fluids for Bacteria and 

 related organisms. 



8. Place some fresh-made hay infusion in three flasks ; 

 boil two of them for three or four minutes, and while 

 one is boiling briskly stop its neck with a plug of 

 cotton-wool : leave the necks of the other two flasks 

 unclosed, and put all three away in a warm place. 



a. In a day or two abundant Bacteria will be found 

 in the unboiled flask. 



h. In the boiled but unclosed flask Bacteria will 

 also appear, but perhaps not quite so soon as 

 in a. 



c. In the flask which has been boiled and kept 

 closed Bacteria will not appear, if the experiment 

 has been properly performed, even if it be kept 

 for many months. 



