BACTERIA AND DISEASE 395 



DEMONSTRATIONS 



170. Place a little yeast upon a microscope slide and examine it 

 with a power of at least 200 diameters. Notice the oval cells from 

 which smaller cells are budding. 



171. Take a bit of mold from cheese or bread and examine it with a 

 power of at least 200 diameters. Notice the strings of mold which 

 appear like very small jointed rods. Notice the collections of round 

 spores at the tops of the projecting stalks. 



172. Place a little hay in a bottle of water and set it in the sun. 

 After a few days, place a drop of the water upon a glass slide and 

 examine it with a power of at least 400 diameters. Notice that 

 numerous bodies of various sizes and shapes are swimming in the 

 drop. These are the animalcules which older books describe. Notice 

 also the real bacteria which appear as the finest kinds of dots and short 

 lines. Most of them are in constant motion. Only a few kinds of 

 bacteria can be recognized by their appearance. 



173. Prepare some gelatine as if for the table, and pour some 

 while hot into a tightly covered dish which has been boiled. Take off 

 the cover for a moment before the class, and, replacing it, set the dish 

 aside for a few days. Then a few specks of mold or of scum will appear 

 upon the surface, each showing where a germ has fallen from the air 

 and multiplied to form the spot. Explain that bacteria are studied in 

 laboratories in much the same way. 



174. Have a druggist prepare a solution of carbolic acid i to 100, 

 and of bichloride of mercury i to 1000. Show the class how they should 

 be used in washing the hands and clothes. Also show the pure drugs, 

 and warn the class against using them in this form. Show also chloride 

 of lime and other common antiseptics. 



REVIEW TOPICS 



1. Describe yeast and give its uses in nature. 



2. Describe mold and give its uses. 



3. Describe bacteria and their relation to decay. 



4. Give the uses of decay. 



5. Show how bacteria can enter the body and how they 



produce sickness. 



