26 ELEMENTARY BIOLOGY. [iV. 



putrefy, so that, as has been well remarked, "putrefaction is a 

 concomitant not of death, but of life." 



Bacteria, like Torulm and Protococci, are not killed by dry- 

 ing up, and from their excessive minuteness they must be 

 carried about still more easily than Torulce are. In fact 

 there is reason to believe that they are very widely diffused 

 through the air, and that they exist in abundance in all 

 ordinary water and on the surface of all vessels that are not 

 chemically clean. They may be readily filtered off from 

 the air, however, by causing it to pass through cotton wool. 



LABORATOEY WORK. 



1. Infuse some hay in warm water for half an hour — 

 filter, and set aside the filtrate : note the changes 

 which go on in it — at first clear, in 24 or 36 hours it 

 becomes turbid ; later on, a scum forms on the sur- 

 face and the infusion acquires a putrefactive odour. 



2. Rub some gamboge down in water and examine a 

 drop of the mixture with a high power : avoid all 

 currents in the fluid and watch the Brownian move- 

 ments ; note that they are simply oscillatory — not 

 translative. 



3. Take a drop of fluid from a turbid hay infusion-^ 

 and examine it, using the highest power you have ; in 

 it will be found multitudes of 



Moving Bacteria. Note their — ■ 



a. Form; elliptic or rodlike — sometimes forming 

 short (2 — 8) jointed rows. 



