BACTERIA. 



outside the front door is a habit to which 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 



