BACTERIA. 
3i 
outside the front door is a habit to whicfi all chil¬ 
dren should be trained. Adults should think what it 
means to bring street filth into the dry, warm house. 
If all coats, dresses, etc., worn on the street could be 
brushed out of doors still another fruitful source of 
dangerous dust would be avoided. House air is 
found to contain thousands of bacteria, where out-of- 
door air may have only hundreds, because moist sur¬ 
faces catch and hold them. Sunlight and large 
amounts of fresh air tend to kill them. The house has 
less fresh air, less sunshine, and it is filled more or 
less with dry, rough furnishings, which add to the dust 
and all tend to hinder its removal and to lessen the 
chances of disinfection. 
In the laboratory bacteria are studied in many 
ways. Under the microscope is noted their shape and 
size; what kind, and the rapidity of motion, if any; 
how they tend to arrange themselves upon division; 
whether spores are formed or not. 
From plate and other cultures can be seen the 
shape and color of the colony; whether they grow 
best on the surface, in much air, or below the surface 
where air is excluded; whether the temperature of 
the room is more favorable than that of the incubator, 
which is much higher and represents more nearly 
the conditions inside of our bodies. 
Some of the bacteria secrete an acid which lique¬ 
fies the gelatine on which they may be growing. This 
acidity can be detected by litmus paper. Some pro¬ 
duce a gas when grown in a sugary solution, others 
Laboratory 
Study 
Secretions 
