iv.] BACTERIA. 29 



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. 



<? Spirochaete. 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 and continue to boil for a minute or 

 two: leave the necks of the other two flasks un- 

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



a. In a day or two abundant Bacteria will be 

 found in the unboiled flask. 



b. 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 experi- 

 ment has been properly performed, even if it 

 be kept for many months. 



