Putrefaction 
12 HOUSEHOLD BACTERIOLOGY. 
and the hairy or velvety ones. Look at the garden 
through a magnifying glass, if possible; watch every 
change; write down an accurate and full account as 
to time, appearance, conditions of temperature, light, 
etc. Then change the conditions. Put the dust- 
garden into the refrigerator, shut it into a box, etc. 
See how the colonies are affected by each new condi¬ 
tion or by any two combined. 
If a compound miscroscope can be used, touch the 
point of a needle to pne of the spots and place the 
speck of matter taken up on a clean glass slide. Put 
on a drop of cool boiled water, and over this a 
cover glass; examine carefully for shape and motion; 
draw what is seen. In this way examine the differ¬ 
ent colonies to see if the forms in all are of the same 
shape. 
Let the dust garden grow for a week or more, then 
gently raise the cover, smelling of the contents, and 
as v this is done, if the growth is sufficiently far ad¬ 
vanced, there will be sensible proof that dust-plants 
may cause putrefaction. The next time you are 
tempted to leave a piece of meat exposed, remember 
the dust-garden, and cover the meat with a cloth to 
keep out dust. 
Figures 4 and 5 are photographs of such dust-gar¬ 
dens after more than two weeks’ growth. The prin¬ 
cipal colonies of molds are marked a, and those 
marked b are colonies of bacteria. In Fig. 5 the row 
of cdlonies marked b' shows well how thickly they 
