202 METHODS IN PLANT HISTOLOGY 



not contribute much to our knowledge of the internal structure of 

 bacteria. 



The methods given here will merely enable the student to study the 

 form and size of those bacteria which are more easily demonstrated. 



Foul water at the outlets of sewers and such places will usually 

 afford an abundance of Coccus, Bacillus, Spirillum, and Beggiatoa 

 forms. Place a drop of water on a slide, heat it gently until the water 

 evaporates, then stain with fuchsin or methyl violet, dehydrate, clear 

 in xylol, and mount in balsam. 



The hay infusion is a time-honored method for securing bacteria for 

 study. Pour hot water on a handful of hay, and filter the fluid through 

 blotting paper. Place the fluid in a glass dish, and cover with a piece of 

 glass to keep out the dust. When the fluid begins to appear turbid, 

 bacteria will be abundant. The active movements are easily observed 

 in a mount from the turbid water. As the bacteria pass into the rest- 

 ing condition, they form a scum on the surface of the water. Usually, 

 the first to appear is a somewhat rod-shaped form, the Bacterium 

 termo of the older texts. Spirillum and Coccus forms often appear 

 later. Scrape the inside of your cheek with your finger nail and you 

 are almost sure to find some bacteria. If you let your teeth go without 

 brushing for 24 hours you can get bacteria by scraping your teeth 

 with your finger nail. Throw flies or other insects into water from a 

 pond or ditch and bacteria will soon appear. 



From such material or from vigorous cultures smear a little on the 

 sUde and allow it to dry for 24 hours in a warm place, free from dust; 

 or, if you are in a hurry, dry it by passing it several times over the 

 flame of a Bunsen burner. Then try the following rapid method: 



1. Place on a clean cover a drop of water containing the bacteria and dry 

 completely in a flame or on a hot plate. 



2. Stain 2-5 minutes in gentian violet or methyl violet. 



3. Rinse quickly in water. 



4. Dip into 95 per cent alcohol to reduce the stain. 



5. Remove most of the alcohol by touching a corner of the cover with filter 

 paper and then dry completely by passing through a flame. 



6. Mount in balsam. 



Ciha of bacteria can be stained in various ways. In the hay infusion, 

 the first form to appear is likely to be one which goes under the name 

 of Bacterium termo. It is a harmless ciliated form. Bacillus tijphosis, 

 the bacillus of typhoid, is a good ciliated form; but students had 



