IV.] BACTERIA. 17 



Bacteria, like Torula and Protococci, are not killed by 

 drying up, and from their excessive minuteness they must 

 be carried about still more easily than Torulct 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. 



LABORATORY 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 highesj 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. 



b. Size; breadth, very small but pretty constant; 

 length, varying, but several times greater than 

 their breadth: measure. 



