CRYPTOGAMS 307 
potatc in (2), where the liquid was dropped? Are they more, or less 
abundant than in (1)? Since cotton wool is entirely impervious to the 
smallest microérganisms known, would ycu judge from this experiment 
that bacteria can gei into any place unless carried there by the air, or by 
some other means? 
ExpEriment 94. CAN BACTERIA BE CARRIED BY PURE AIR? — On a 
warm (and preferably cloudy) day, put a slice of potato on a plate, and 
leave uncovered in an unused room or closet, free from dust, and kept 
carefully closed. Put another slice arranged in exactly the same way 
in an open window on a dusty street, or in a room that is used and daily 
swept and dusted. Do bacteria appear in the first plate? In the second ? 
Is air free from dust a good conveyor of bacteria? 
EXPERIMENT 95. WHAT CONDITIONS ARE FAVORABLE TO BACTERIAL 
GRowTH ? — Strain some of your culture liquid into half a dozen small 
bottles of the same size, filling each about half full. Put (1) in a dark, 
cool place — on ice, if the weather is warm; (2) in a dark, warm place; 
(3) in a warm, well-lighted place ; into (4) puta drop of carbolic acid, form- 
alin, corrosive sublimate, or boracic acid, and keep in a dark, warm place. 
Keep (5) in boiling water for half an hour or more, and then place beside 
(2). Keep (6) in a freezing mixture of salt and ice for several hours, then 
place with (2) and (5). Examine all at intervals of from 12 to 24 hours, 
In which bottles is the presence of bacteria indicated by cloudiness of the 
contained liquid, or the formation of a surface film? In which do they 
appear first? In which most abundantly? In which last, or not at all? 
What is the effect of light and darkness on their growth? Of heat and 
cold? Of disinfectants? Name the circumstances that tend to hinder 
their growth, in the order of their efficacy. 
348. Microscopic study of bacteria.— Put a drop of 
hay infusion on a slide and examine with the highest power 
of the microscope. You will see a multitude of very small 
glistening bodies including different kinds of bacteria, a 
majority of which are probably the hay bacillus, B. sub- 
tilis, shown in Figs. 443, 444. Notice that some forms 
move about freely, while others are non-motile. Which 
kind are the more numerous? The motion may be either me- 
chanical, resembling that of the small dust particles we see 
dancing about in the sunshine, or apparently voluntary, 
and caused by the vibration of little whiplike cilia. Can 
you distinguish the two kinds? Try to make out clearly 
